FIELD NOTES AND OBSERVATIONS

 

On this page I hope to present some field experiences, observations, and theories based on those experiences. I also would like to challenge some existing theories and some inaccurate reporting, much of it in so-called professional journals, some of which seem to lack experienced or educated editors, those who seem to have rested on their laurels and take no pride in what they present to the public as FACT. It serves no purpose to present to the public incorrect information or factoids, rather, it is the responsibility of these so-called professionals to do an accurate job, not a sloppy one. But I can only challenge that which I have personal knowledge and experience in that field, so I will not deviate into areas in which I have no expertise.

NEW FINDS: Here are some discoveries which I have made recently, those which have missed publication, and some that haven’t. It remains important to present these facts in some kind of forum, and these days the internet is perfect for this.

Between 2002 and 2005 I took several trips to collect in the Black Hills of South Dakota, specifically in the many pegmatite localities near Custer and Keystone. At the Nickel Plate Mine, near Keystone, the locality in which the mineral arrojadite was first discovered, we spent much time digging through the tailings looking for examples of this mineral. We were rewarded by much arrojadite, some in large cleavable masses up to several pounds each, and measuring several inches across; we also found other phosphates, cassiterite, and discovered two minerals not reported from here previously: first, tapiolite, which was identified by x-ray diffraction at Montana Tech, and ferrocolumbite, which was far easier to identify by habit, morphology, luster, color, hardness, etc.

At the famous Tip Top Mine we found numerous phosphates and other curious minerals, but we found a fist-sized mass of reddish phosphate originally thought to be hureaulite, but on x-ray diffraction identified it as triploidite. This mineral has yet to be found at this locality.

Over a period exceeding 15 years, I have explored an unmapped Tertiary age miarolitic granite located at the extreme southern border of Ravalli County, Montana. I coined the name "Cathedral Rock Pluton" after the only named feature in the area, a prominent granite outcrop located near the eastern extremity of this intrusion. It outcrops at the head of Woods Creek and westward nearly to Reynolds Lake; it extends for several miles into Idaho, but only in places shallowly into Montana. Here, collectors have worked over areas with numerous miarolitic cavities, in a granite very similar to the Sawtooth Batholith or the Lolo Batholith to the north of this area. One place appears to be an aplitic body riddled with cavities; here people have dug hundreds of holes to intersect the smoky quartz-lined vugs. Other minerals we have identified here include: smoky quartz, microcline, albite, magnetite, fluorite, bertrandite, zinnwaldite, zircon, and epidote. The zircon crystals are small but bright green; some of the microcline is found in Baveno twins, well-formed and sharp, and some highly prismatic.

In the Boulder Batholith, new discoveries are being made all the time. Every season, new finds are made, and new specimens are brought to light. A few years ago, a pegmatite east of Butte in the Whiskey Gulch area produced smoky quartz crystals with a thin layer of pale amethyst overgrown, containing fine acicular inclusions of the mineral lepidocrocite. These appear silvery and highly metallic in reflected light, but are blood-red in transmitted light. Similarly, a locality just south of Butte has produced many fine amethyst crystals, often with platy inclusions of hematite.

Local collector Greg Schmaus discovered a pegmatite with fine yellow crystals of fluorapatite, some measuring up to over two inches in length. These are a little dull in luster but very well-formed, with terminations exhibiting the basal pinacoid and the first- and second-order pyramids. Nearby he found another vug with large titanite crystals, up to four inches across. In both cases, smoky quartz and fine, acicular schorl tourmaline were associated.

Another local fellow, Zach Johnson, has been successfully digging the pegmatites now for several years; he has found huge smoky quartz crystals, many fine quartz-feldspar matrices, large schorls, at least one five-inch titanite, and a number of superb allanite crystals. The latter are euhedral, vug specimens with sharply-formed crystal faces, but dull luster; they are distinctly terminated, twinned, and one was entirely euhedral, terminated at both ends (a "floater"). The allanites average about 1-1/2 inches in length, and an inch in width.

Another recent development is the purchase of the old "Glittering Hill" claim by this author; this was made earlier in 2007, enabling me to do some development work this past summer. This was originally staked by Oscar Schnadel (deceased) in the 1930’s, for silica; he drove an adit below the outcrop to intersect the vein at depth, no realizing the horizontal lie of the pegmatite deposit (the adit passed completely under the structure without ever hitting the quartz or the pegmatite itself). Originally, the upper feldspar zone (pocket-bearing) was completely and entirely weathered away, not only exposing the massive quartz core, but distributing the contents of the pocket zone all around and below the outcrop. The subsequent liberation and exposure of the many pockets resulted in a veneer of shiny quartz crystals scattered throughout the soil below the outcrop, hence the name "Glittering Hill". The claim was taken over by his two partners after he passed, and they abandoned it around 1996 when the last owner staked over it, re-naming it the "Hilltop Claim". After Mike Sprunger worked it for several years, I gained permission to do limited digging there, and opened the very first in situ pockets ever found there as of that date. A number of fine, pale amethyst scepters were found, along with parallel overgrowths typical of the area’s so-called "eyebrow" pegmatites/amethyst deposits.

After some time, Mike decided that he couldn’t make a go of this deposit, financially speaking, so we worked out a price and now I am developing it. Last summer we opened several fairly large pockets, with scattered amethyst and quartz crystals; the vugs here are typically choked with pocket material, but quartz is not the primary mineral (mostly feldspar). Odd and unusual scepters are common, along with parallel overgrowth; some small scepters are found growing on a matrix of corroded microcline, many in parallel position. There does not seem to be any albite here, but we have found and identified malachite and ilmenite in the wallrock. More will follow on this project!

I need to ferret out some errors I find very disturbing, since they are published and those who would read these errors might actually believe them to be factual. Primarily, I wish to expose one particular article written about the Butte, Montana mining district, that has been accepted by many as accurate, but the facts need to be set straight once and for all. The article I’m referring to is the one that appeared in the Mineralogical Record, January-February 2002, as written by Jerry Lorengo and Robert Jenkins. In spite of repeated attempts to assist in the accuracy of this paper, the authors refused flatly to allow any input or assistance, so I lay the blame solely upon their shoulders. One of the most glaring inaccuracies is their blanket claim that virtually ALL smoky quartz and amethyst labeled "Butte" is not from Butte, but from the surrounding area; this is patently untrue and a real problem since many will actually believe this. Not only did many of the miners themselves report finding these minerals in the underground mines (as taken from countless interviews I had with many miners over a period of 25 years or more), but the evidence is still out there, where pockets of quartz, feldspar, tourmaline, and other pegmatite minerals are found literally within the city limits of Butte. Even early maps of the area show large aplite-pegmatite bodies just west of town, in the center of the silver mining district. Similar aplites and pegmatites are found on Timber Butte, east of Butte at the base of the East Ridge, adjacent to the current East Continental Pit, also around the Big Butte and in Walkerville, all part of the central mining district and well within the Butte mining district proper. Weed (1912) in his "Geology and Ore Deposits of the Butte District, Montana" states that these minerals were found even at some depth in the Butte mines. I would like to add here that this was one of the references the authors used in their paper; apparently they either didn’t read it or chose to ignore it as a fact. Nonetheless, pegmatite minerals ARE from Butte, so don’t go out and change your labels!

Other errors and/or omissions are clearly evident in this work: while I find the article generally well-written, and the area’s history colorfully presented, the geology bears much better accuracy and detail than is presented here. I recommend Weed’s paper or the one published in 1973 about Butte by the Anaconda Company titled "Butte Field Meeting". The M.R. article doesn’t do much for the Butte deposits, even in general (it’s not written by geologists, just mineral collectors). But there one very notable mistake all should be made aware of: on page 42, Figure 39: shows a barite crystal cluster reportedly from the Mountain Con Mine in Butte, when in fact, this specimen is clearly from the famous Indian Head Rock deposit near Basin, about 25 miles north of Butte (apparently George Loud got cheated GOOD). The specimen illustrated above this one, Figure 38, is from Butte.

I would also like to point out that the authors both complained to me that the selection of mineral photos they presented to the editor, Wendell Wilson, were mostly rejected by him, in favor of ones he had chosen. While many of the covellite pictures were really great, and some of the enargite, rhodocrosite, and pyrites were also great, many of the photos were very substandard and really not representative of what has been found in Butte. For starters, not a single picture was taken from the Montana Tech Mineral Museum’s collection, which holds some of the finest Butte specimens in the world. Other private collectors were similarly snubbed, even though many of them had superb examples to offer up for photography. Instead, a series of poor examples and some truly bad photography are presented here, and Butte residents and collectors alike were frankly, offended. For starters, take a look at the Figure 46: this shows a bunch of platy covellite crystals, all badly sheared off, even though replaced by chalcocite, a pretty ugly, damaged specimen. They could have easily come up with a much better example. Another real dud is Figure 65, which does little to show the morphology of enargite. Next, see Figure 66: a coating of luzonite?? This picture illustrates practically nothing of importance or significance. Below it, Figure 68 is calcite on galena and sphalerite, but none of these minerals are either good examples or representative of Butte. Figure 74 shows a very ordinary quartz crystal matrix; many far better examples exist, including one spectacular plate mined in the late 1980’s in the Lexington Tunnel and currently owned by Pete Knudsen.

A great example of where this article put its emphasis on is illustrated by the smithsonite specimen in Figure 80: since only one or two smithsonites were ever found in Butte, how is this representative of the deposit? While certainly a curiosity, it does little to add to the incredible legacy of those minerals for which Butte is truly famous. Where are the pictures of the fine fluorapatites found in these mines? One of the authors made vague and out-of-context comparisons when I suggested that fine fluorapatites were found in Butte mines, in great numbers (although not commonly recognized). Also glaringly omitted were the fine euhedral crystals of wavellite, a mineral not commonly found as distinct crystals. What happened here guys?

Figure 82 is unbelievably bad; either the specimen has little to offer or the picture is that bad, but it also does nothing here to illustrate the legacy of Butte minerals. The next one is equally bad; Figure 83 shows a broken enargite replaced by tennantite; couldn’t they find a better example? In Figure 51, the picture is great, but the scale of the colusites is so small compared to the picture as to render them almost invisible. It does nothing to inform or educate the viewer as to the morphology or appearance of the mineral colusite (which was first found here and named after Butte’s Colusa Mine!)

Another glaring omission was that pertaining to pseudomorphs found in Butte. While mentioned singularly in the text of some minerals and in a few photos, Butte has nonetheless produced a prodigious quantity of curious pseudomorphs, many which are as complex and quixotic as to defy accurate description. Given the extent of secondary mineralization and enrichment, much of what was found in upper zones was entirely replaced by other minerals, yielding a whole variety of these curious specimens, way too many to mention here. Some one out there needs to do a little research into this phenomenon as it pertains to the Butte deposits, worthy of a PhD thesis at any university. The author’s failure to recognize the importance of this topic was truly criminal. They also made the statement that finer crystals of covellite were found at Summitville, Colorado, which is just not accurate at all, given the sheer amount and size of Butte specimens when compared to those of Colorado. I guess another thing they never saw were really good Butte covellites, or they wouldn’t have made this erroneous statement.

To sum it all up, this article does a great injustice to the geology and mineralogy of Butte. It’s also a good example of the kind of editing and publishing that Wendell Wilson is perpetuating on his readers, the kind that allows glaring errors and omissions and selects specimens and pictures of samples not deserving of any particular note, but are apparently used to fulfill some kind of public recognition for select individuals. For this and other reasons, I quit subscribing many years ago, and would like to encourage all who read this to do the same!

One more note in this vein: another article that mentions something that is patently false is in the Mineralogical Record, May-June 1993: the paper on the minerals of the Sawtooth Batholith by Menzies and Boggs contains a photo on page 195, Figure 13, depicting a "pseudomorph of topaz and quartz after microcline". This specimen is corroded microcline with little of its original form left, encrusted with tiny topaz and quartz crystals, which grow in completely random orientation on the remaining surfaces of the microcline crystal. Since the encrustation hardly follows the shape or form of the original crystal, it can hardly qualify as a true pseudomorph. This is merely an ordinary encrustation of an early mineral followed by a secondary growth. In some texts, there are references to "encrustation pseudomorphs", while other do not mention this at all. Since many encrustations over other crystals do not involve any real replacement of the earlier mineral, I don’t believe they qualify as a pseudomorph, even remotely. A good example of a true pseudomorph is that of goethite replacing pyrite: the sulfur has been replaced by hydroxyl ions, completely changing the original chemical composition. In the case of the specimen in question, no replacement has taken place, although it is highly likely that the topaz and quartz formed at the expense of the microcline’s dissolution.

Other errors are found in this article: this author has done considerable work on the micas found in the miarolitic cavities, including dozens of x-ray diffractions on various samples, and from numerous different pockets. Despite what is reported in this article, absolutely NO muscovite or masutomilite has ever been identified. All of the pocket mica is zinnwaldite, some with more or less traces of manganese, but samples from the pocket Boggs analyzed were done with a scanning electron microscope and this method only detects the presence of most elements, but nothing about the crystal structure or the d-spacing that distinguishes on mineral species from another. I obtained samples from the supposed masutomilite pocket and they were x-rayed at Weber State University and identified as zinnwaldite.

Another issue concerning the mineralogy of the Sawtooth Batholith should be discussed here, as it also remains a controversy: Idaho collector Geary Murdock, who passed away in 2002, once sold prodigious amounts of fine aquamarines and other miarolitic granite minerals, all labeled under the umbrella of a location given as "Centerville, Boise County, Idaho". While there is indeed an aquamarine locality in at least one place (specifically, a claim once held by Murdock on the lower portion of Swede Creek, between Centerville and Placerville), this small locality produced a number of dull, somewhat water-worn aquamarine crystals that had apparently weathered from a pegmatite adjacent to the creek. What little research this author was able to accomplish yields this: originally the creek had been worked for placer gold in the 1860’s (or perhaps somewhat later), when at least some of these aquamarines had been uncovered. It remained unknown until sometime in the mid 1970’s when a couple of rockhounds from Oregon stumbled on to this deposit, digging there and recovering a quantity of good material. It has been stated that Murdock had actually bought all of the Centerville material he was later to sell, and he staked over the site but worked it without finding anything additional. Aquamarine crystals from this site are typically dull in luster, displaying simple pedion terminations.

Murdock did do extensive exploration in the Sawtooth Mountains, as he once lived in Stanley, the nearest town to the wilderness area. At least one other collector had explored with Murdock, the late Rich Kosnar of Colorado. Murdock had discovered at least one spectacular aquamarine deposit, which according to him (personal communication, 1983) was entirely weathered out, so that all the pocket contents were distributed throughout the soil profile below the pocket, which was by then, empty. Besides the aquas, which were very lustrous and terminated by a combination of the pedion and the first- and second-order pyramids, he found a suite of other spectacular mineral specimens, including spessartine garnets of impressive size, fine, large hematite rosettes, microcline, smoky quartz, and a new variety of the mineral carpholite. All of these were subsequently marketed as being fro "Centerville"; it has been surmised that he did this to avoid trouble with the law as pertaining to the commercial sales of material removed from a federal wilderness area.

A number of years passed, and while many questioned the authenticity of the locality labeling, nothing specific was done until the new carpholite variety was properly analyzed and identified in the Canadian Mineralogist, Vol. 42, 2004. But the locality was given as in the "Sawtooth Batholith, Centerville, Boise Co., Idaho". This only served to perpetuate the myth about this obscure (and very small) locality. This author had researched this supposed site, including one trip to there, and challenged the authors of the article concerning that locality, as Centerville is over 50 miles west of the known Sawtooth Batholith. Furthermore, the Centerville locality is a pegmatite located in the Cretaceous Idaho Batholith, and while the pegmatite is likely to be of Tertiary age, the area is underlain by a granitic intrusion that has no correlation to the Sawtooth Batholith at all, at least what is evident there. All evidence points to the origin of the potassic-carpholite as being from the miarolitic cavities in the Sawtooth Batholith, as the only other discovery of this mineral was made here by this author in 1982. Given its relative rarity, it is unlikely that this species has ever been found outside the Sawtooth granite (where other carpholite has been found as well, the more common variety).

What lends further credence to this deception is the claim that Murdock made concerning his "discovery" of yellow beryl in the Sawtooths: reported in Sinkankas’ "Gemstones of North America, Vol. III", the occurrence of yellow beryl was given by both Murdock and Kosnar. Recently this author obtained one of these suspect crystals (as NO other color of beryl other than blue has ever been observed anywhere in the Sawtooth Mountains); this proved to be easily identified by a simple measurement of refractive indices, which resulted in the identification of the specimen as fluorapatites (clearly and unmistakably from Durango, Mexico). Since this was obviously never found anywhere near Idaho, much less in the Sawtooths, the deception pointed out clearly the deceptive practices Murdock had engaged in. His credibility was reduced even further. This author published a retraction of the "mythical" Centerville locality in the June, 2005 issue of the Canadian Mineralogist.

 

ON THE GENERATION OF PEGMATITE POCKETS AND MIAROLITIC CAVITIES:

Author John Sinkankas postulated a theory based on his observations of pockets in the Himalaya and other pegmatite mines, which essentially proposed an "open system" theory for the growth and crystallization of pocket minerals. He astutely observed that in many pockets, the volume of crystals contained within far exceeded the ability of the enclosed mineralizing fluid to hold this amount of material in solution, so therefore the system must have been re-opened and additional fluids added to grow such a volume. This would be true if we subscribe to the "hydrothermal" origin of all minerals, but it can be shown that there are way too many problems with the open system theory to support it.

Many pegmatite pockets and miarolitic cavities are literally "choked" with crystals, which seem to occupy every possible space within the pocket opening. It does seem improbable that fluids or volatiles trapped in the system could hold enough ions in solution to precipitate the given volume of solids contained. Sinkankas suggests (personal communication, 1997) that the system undergoes a "re-opening" that allows addition fluids to enter or circulate through the system, depositing additional material. He uses the famous Himalaya Mine as an example, which has been studied well enough to serve as a great example of this problem. But the pegmatite vein itself serves more to disprove this theory rather than to support it.

For starters, we must examine this solution through ordinary physics and rock mechanics: in order to re-open the vein, it must be solid and crystallized or shearing/fracture/rupture of the rock can take place. Molten magma, whether fluid or plastic, will not break or shear but solid rock will. This leads to the problem of actually splitting the system across its center line, allowing the outside fluids to enter and pass through the central pocket zone. Otherwise, we have to open EACH individual pocket to satisfy this postulate, which is even more difficult than splitting the entire pegmatite along its centerline. This would basically defy the laws of physics and what we currently understand about rock mechanics, where rock in failure will break into a conjugate set of fractures, not just along a single line. Given the sheer length and down-dip dimensions of the Himalaya dike, it would be impossible to split it along the centerline completely; somewhere along the way it would deviate and eventually cut across the dike and past its margins or contacts. Also, there is no evidence whatsoever of the second or conjugate set of fractures, which naturally would be at an angle of approximately 35 degrees to the primary fracture line. There is overwhelming evidence that such fracturing never took place, that no re-opening of the vein or system occurred.

In a geological environment, it is quite common for competent rock to be broken or fractured; numerous to countless examples of differential rock movement exist on every continent. The argument here is not that it can occur, but what evidence is there that it DID occur. When solid rock is broken or sheared, fragments and bits of the adjacent rock are incorporated into the shear zone, sometimes becoming lithified in which case it is called a breccia. Sometimes the rock along the shear plane is ground into a fine powder, known as fault gouge, and if lithified, it is called mylonite. All of these would indicate the suggested re-opening, but no breccia, fault gouge, or mylonite is evident in the Himalaya Mine’s pocket zone to suggest or prove this event took place. Furthermore, it would be almost impossible to open up such an extensive system without some differential movement along the shear plane; to the contrary, structures from both contacts extend toward the centerline showing no interruption in their growth.

This latter point serves to illustrate that growth from the wallrock contacts inward clearly show that there was no interruption of growth during the consolidation of the body. "Rods" of tourmaline that nucleate early at or near the contacts, start as black schorl and slowly increase in grain size as the body cools at a lesser speed, finally increasing to maximum diameter at the border or edges of the pocket opening, where they grow uninterrupted into the vug as lithia tourmaline. These rods are very common in most tourmaline-rich pegmatites; they often grow perpendicular to the wallrock contacts and project into the pegmatite body in a direction towards the centerline. If the pocket system were to be re-opened, these rods would exhibit some interruption in growth, but no evidence of this exists.

Another problem with this theory lies in the source, path, and expelled material from this mineralizing or hydrothermal fluid: if this event did occur, then what is the source of the fluid that contains only a specific liquid that has the necessary ions to grow just those minerals found in that very singular environment? Since no evidence of the shear of the rock is apparent, how does this fluid come to enter the vug, and where does it eventually go? Is there only one singular, second injection that adds the final amount needed, or does this fluid pass through the system and continually precipitate the necessary ions until all the crystals are grown and the system becomes sealed off? Since pockets invariably exhibit no active openings when found and excavated, then this theory must include the fact that once re-opened, they end up sealed in the end. This would make it physically impossible for the fluids to circulate through some kind of interconnecting conduit, since at some point each individual cavity is sealed off.

Another flaw with this theory lies in the alteration that invariably accompanies the introduction of hot, hydrothermal mineralizing solutions: wherever they pass through, they alter adjacent rock by adding additional elements and replacing earlier, less stable minerals. Alteration zones or haloes are proof of such fluids, but in the case of pegmatites, no altered zones appear except around pocket openings, where these fluids are not only trapped, they eventually penetrate adjacent rock and alter it. There are other types of alteration evident in many pegmatites, but the point here is there’s no evidence of the shearing or opening of these systems, and any alteration from such introduced material is not apparent.

I have to state here that all of this is based on observations that I have made in the field; over a period covering field collecting for nearly three decades, I have discovered, opened, and observed hundreds of pegmatite pockets, and literally thousands of miarolitic cavities. None of the miarolitic cavities I saw had any type of conduit showing from any direction, for any length, with the exception of a couple that seemed to have formed along horizontal joint surfaces, but these were rare and exceptional. All others were totally isolated in the granitic host rock, with no channels or conduits exposed, either leading in or out of the vug opening. The laws of probability and statistics dictates that after observing at least some of these systems, at least one would be exposed across one of these conduits, but every vug I observed showed no evidence of this at all, leading to the inevitable conclusion that these systems must be closed systems. If this is the case, then how does so much material come to grow in these relatively small systems?

The main problem lies in the so-called hydrothermal origin of crystal growth: it is believed that when such vug openings are found, that the fluids contained within are the source for mineral growth or precipitation, that is, the liquids held in the opening contained dissolved ions that precipitate out of solution, growing the crystals that line the vugs. But it is clear that no such solution, no matter what the conditions, can hold the sheer volume of solids that are found in many pockets. Is it possible that the fluids are not the source in this case? What of the clearly magmatic nature of granites and granitic pegmatites? It is generally accepted that pegmatites are derived from molten granite magma and injected or squeezed into surrounding rock units or even into the granite itself. The accepted theory of pegmatitic crystallization states that it starts along wallrock contacts, cooling rapidly into small grains, then continuing inward toward the centerline, gradually cooling as growth rate decreases and grain size increases. Theoretically, the largest crystals are found near or at the center or core of a pegmatite; in most cases the center in occupied by a mass of solid quartz, which is the last mineral to form according to Bowen’s reaction series.

As the reaction proceeds, those elements used in the formation of the earlier minerals become depleted, slowing increasing the percentage of the elements that remain. This process progresses and other elements are consumed to form the intermediate minerals, continuing to enrich the remaining magma in the more stable elements. Eventually, all that remains are the last minerals to form, and those volatile elements that do not bond with the others to form solids. These volatiles eventually become trapped in the areas of lowest pressure as immiscible liquid/gas. In some pegmatites, the last two phases of solid growth are the formation of massive, coarse-grained microcline crystals, followed by the solid quartz core, into which the feldspar crystals protrude at roughly perpendicular orientation to the wallrock contacts. Where these prismatic crystals grow together in a jumble of crossed and intersecting "logs" (mostly Baveno twins, quite euhedral but encased in solid quartz), the volatiles becomes trapped in areas where two or more of these prisms intersect, in-between and underneath them.

The end result is that the source of the material that grows into the pocket openings is from the wallrock magma, not from the trapped volatiles. It is apparent that those volatiles do have some influence on growth, but to what extent is not exactly clear. First, the crystals begin to grow euhedrally into the opening, uninterrupted and uninhibited by adjacent crystals; the growth is facilitated by this aqueous solution, as it is clearly physically different than the same minerals growing in the adjacent wallrock. Secondary growth, however, may be due entirely to the action of those volatiles on the primary minerals (such as microcline, albite, tourmaline, topaz, beryl, garnet, and others). A good example of this secondary hydrothermal alteration would be the dissolution of beryl and the subsequent formation of bertrandite at its expense.

One article in the Mineralogical Record (on Colorado pegmatites) described the genesis of mineral growth as first, a primary growth of quartz and feldspar minerals followed by a "re-opening" of the system in order to introduce a secondary growth of fluorite. Why does this become necessary? Is it not possible (and easier!) for the primary crystals to grow into the vug, containing fluids and gases rich in calcium and fluorine, to be followed by a final phase of fluorite crystallization merely using materials already present in the volatiles? Because of the difficulties described above involved in re-opening these enclosed systems, it is clear that such secondary mineralization could be achieved merely by differences in stabilities for each mineral and in what environment it will grow (or exist) in.

Because the conditions for an open system are clearly not possible or at least evident, it then becomes the realm of a closed-system process. There is clearly enough volume of material supplied by the magma melt to form the volume of crystals found in any pocket. It is the exact mechanism how this happens that is not completely understood.

POCKET WALLROCK FRACTURING

Another issue bandied about by some authors (and published by such "professional" journals like the Mineralogical Record), is that of the so-called "explosive event" observed in so many pockets. This is another misconception proposed and theorized by those who clearly have no background in physics, physical chemistry, mineralogy, or geology. The issue here is that many pockets have extensive fracture zones surrounding them, primarily in the form of radiating crack extending into the surrounding pegmatite wallrock, in roughly perpendicular orientation to the pocket walls. Some people have taken to interpret this as an explosive event without considering that this is not a reasonable explanation for at least two reasons: first, this is not the only mechanism that could possibly result in this configuration. Second, the evidence shows that the force required to achieve this is directional and not random. The evidence shows clearly that if there was indeed an explosive event, the resulting release of force would shatter all the crystals in the area as well as the wallrock! Since most pockets contain fine crystals, albeit often dissociated from the wallrock (through other mechanisms, but not "explosive"), they couldn’t have possibly be involved in such a forceful event or they too, would be damaged from the release of such proposed energy. There is clearly a simpler, far more plausible explanation for this phenomenon: in physics and physical chemistry, there is a relationship between pressure, temperature, and volume defined simply as: PV=nRT, known as Boyle’s Law, where P= pressure, V= volume, n= amount (usually in moles), R= a constant, and T= temperature. One tenant to this is that if we now accept the "closed system" of pocket development as described above, then the volume and the amount of the system is fixed or constant. This results in a system that is entirely dependant on pressure and temperature; these functions are then directly proportional.

In such a chemically and physically active system as a pocket filled with crystallizing minerals or solids, with a liquid/gas medium, the bonding energies that create those solids are consumed, sometimes with exothermic results, and sometimes with endothermic results. In other words, heat is both consumed and evolved, depending on which specific reaction is taking place at any given time. Because virtually all crystallization has taken place before this "event" occurs, then it is clear that this happens after most solidification has ceased. An increase in temperature would result in an increase in pressure, and as the system’s volume is fixed, the pressure increases directly and is exerted on the walls outward. The vug or pocket opening it behaves like a pressure vessel, and the force is directed to the walls of the vessel. Essentially, the system now tries to correct its fixed volume by increasing that volume, and if the pressure is great enough, it will increase to a point where it exceeds the strength of the wallrock and it ultimately ruptures. Here, rupture (or failure) is not anything like an explosion, which could be defined as an instantaneous release of energy, but as described above, the result of an explosion would fracture or demolish anything within its immediate realm. Since most pockets hold relatively undamaged crystals, some in extraordinary state of perfection, this simply cannot be the mechanism, but failure or abrupt rupture of the wallrock does satisfy the equation, this is clearly the better of both solutions. Just because the rock is fractured, it doesn’t necessarily mean that it had to "explode".

 

 

THE CASE FOR DISSOLUTION

Another argument that holds little accuracy or practicality has bearing on both subjects discussed above: former curator John Sampson White has argued against the case for dissolution as he presented in Rocks & Minerals (…….). He presents only one instance which he categorically states proves that dissolution is not at work, casting doubt on the entire process in the argument. What he doesn’t consider here is that like other subjects not fully understood, there are other possibilities at work here that could easily explain the mechanism or process. A good scientist will examine a problem from all sides, considering all facets involved, before drawing any conclusions (and certainly before publishing their opinions as FACT, so that others believe what is printed as irrefutable). The same problem in this thinking process extends to all the examples stated above: if they do not prove to be true, but you have published it as FACT in print, then the misconception or falsehood becomes accepted by all who read or pass this misinformation on as a truth. A good example of this would be the "Centerville, Idaho" locality: if it hadn’t been disproved as a myth, then all those who possessed specimens purchased from Mr. Murdock would believe that the material was indeed from Centerville, which most of it is simply not.

I won’t go into the exact details of Mr. White’s article, as the reader can do this themselves, but basically he shows some oddly etched tourmaline crystals and claims that they are proof positive that dissolution was not at work here. Apparently he does not understand the basic concept of stability regions, which are areas of a substance’s stability (or physical existence) based on specific conditions or properties, which include temperature, pressure, pH of the solution, eH, activity, concentration, and a number of other physical/chemical conditions which are specific to each compound and it’s components. Essentially this defines at which conditions a substance will form or become unstable; in that region a substance will be stable, outside it will dissolve or disintegrate. Since a mineral like tourmaline often occurs in different subspecies and therefore often observed as different colors, each one of these is subject to different stabilities, in regions where that specific subspecies is stable, and outside that region where it is unstable. Once the conditions are changed, and a new region is entered, then the mineral or substance becomes unstable, it begins to break down. In the example Mr. White gives, the base of the tourmaline crystals is etched while other portions are not. This only indicates that the earlier formation of green tourmaline is less stable than the later pink tourmaline, which has overgrown the green portion. The green by definition formed earlier by its difference in stability (versus the pink), and is therefore somewhat less stable, rendering it easier to dissolve or become unstable than the later, more stable pink tourmaline. This difference doesn’t have to be great, just enough to allow the green tourmaline to dissolve preferentially over the pink, which could easily remain in a region of stability while the green has passed out of its region of stability. But Mr. White doesn’t even propose a reasonable solution for this, just his lack of understanding of this very simple mechanism.

This problem also extends into the process of crystallization that yields crystals that appeared to be etched, with surfaces exhibiting alternating growth patterns (a good example of this phenomenon is the vug crystals of spessartine garnet found in many pegmatite pockets). Here what we are seeing is an example of what happens when a mineral grows in an environment that alternates or crosses one of the stability regions repeatedly, showing a pattern of oscillating growth and dissolution. The result is a crystal that grows, reverses, grows, reverses, etc. resulting in a surface pattern that is described often as "etched". This is contrasted by those crystals that grow and then the growth reverses once to actually etch the surface. The oscillating growth at question here shows repeated reversals and sometimes is called "hopper" growth as well. I propose here that this phenomenon be referred to as "oscillatory growth" rather than "etching".