Chapter 4 , page 3
More Q & A about Quartz crystals
Q. I've been reading Miser and Engels, both think that the heat associated with quartz crystal formation in the Ouachitas came from magmas. What is the current thinking on this? It would seem to me that the heat from orogeny might be enough and would explain the very large area of deposits. I am not denying that magma might play a factor in some areas, especially Little Rock. Kenneth Quinn.
A. Ken,
Over the years I have thought much about this entire situation, and I am going to tell you that I do not believe any magmatic source was directly related. There are several geologic lines of evidence to support my conclusion and I will present some of them right now:
1) The age dates on the quartz mineralization are all wrong for any known magmatic event in Arkansas. We have magmatic basement rocks that are Pre-Cambrian to Cambrian. We have some Triassic diabasic rocks in extreme southwestern Arkansas and we have many Cretaceous intrusions that range in age from around 108 to 87 million years in age. The dates on the bulk of the quartz veins fall in around Late Pennsylvanian to Early Permian. So none of the known magmatic rocks fit time-wise.
2) The chemistry of most of the igneous rocks is wrong. Here we see a predominantly Cretaceous sub-silicic igneous suite obviously derived from mantle olivine basalts and even mid-mantle lamproites (ultrapotassic rocks), not a granite in the batch. Not even a granodiorite or diorite. It seems too difficult to me to mobilize so much silica from a silica-poor host rock.
3) Granites are known to have quartz veins associated with them -- I'll give you that. Look at those in California and Colorado, and even Nevada. And they have something else associated with quartz veins originating from granite, native gold. We have had over a 100 years of quartz mining in this state and no one has yet to show us a quartz specimen with native gold that came from Arkansas, although I did examinine a faked specimen one time (but that's another story altogether).
So I feel confident that granite is out as a potential source, but where does that leave us in our search for the source of the silica-rich hot solutions? Well, I have thought about that, too. I believe the strongest evidence points toward formational brines and fluids forced out during the Ouachita orogeny (mountain-building process) which took place some 286 million years ago. This is in the correct time frame for the known age of the bulk of the quartz mineralization. Just a few miles west of Arkansas, in McCurtain County, OK, there was a well drilled that went to over 10,000 feet in depth. Below 2,000 feet, the units were described as greenschist facies. We do not see this exposed on the surface in Arkansas, but I feel that it may be there in the subsurface. Kern Jackson from Fayetteville reported years ago on very low grade metamorphic effects (zeolite facies) of some of the surface units.
What is the most mobile phase during any regional metamorphic event? Water, good old H2O. And other very mobile phases at even low grades of metamorphism include silica, mercury, antimony, lead, zinc, and other base metals. This, I feel, is the origin of the hot silica-rich salty fluids that moved up the pressure gradient to the near-surface units where it dumped its chemicals as mineral deposits. The base metal deposits of the Ouachita Mountains of Arkansas always have quartz veining associated with them. We have a minor anomaly around Magnet Cove and Potash Sulphur Springs bodies, but these mineral deposits are unusual, being vanadium- and titanium-rich, obviously sourced from the intrusions and not concentrated from surrounding country rock.
So to answer your question directly, I think the solutions that the quartz veins in the Ouachita Mountains formed from are attributable to metamorphic or deformational pressure sweatout, not any magmatic process.Mike H.
PS: Good question, got anymore?!?
Q. Mr. Howard, you come highly recommended. Could you please tell me the difference between lascas quartz and quartz? And does a simple test exist to check for lascas quartz. I would really appreciate any help in this area, and any information on lascas.
Brian Wodetzki, Plant Manager , Kemwater North America
A. Dear Brian,
Lascas is the industrial term for a product made from milky vein quartz. The lascas is produced from hydrothermal vein deposits that developed in the Ouachita Mountains at the end of the Ouachita orogeny (mountain building process) at the end of Paleozoic time, some 286 million years ago. It consists of cleaned (of clay and iron and manganese staining) milky to clear quartz that has been graded for chemical purity.
The milky vein quartz along with any rock crystal is first mined, and crushed to about 1.25 to 1.5 inch size, and washed over screens to remove the bulk clay and fines. Then it is heated in an oxalic acid bath to remove any iron or manganese staining and, after cooling, is rinsed to remove the acid. It is then dried and graded.
Grading is done visually over special light tables, where lower grade quartz with matrix attached and off color quartz is removed by hand. It is separated into 4 grades, the highest purity being water clear, then transparent milky, then two lower grades of milky. The only difference between lascas and any ungraded piece of quartz is that the lascas consistently has very low alkali and aluminum content.
Lascas is what is used as the chemical feedstock in the industrial process of growing synthetic quartz. It must meet the specifications of the user, or it will not grow the proper product. If you had a deposit of quartz which you think might have lascas applications, you must have the quartz tested for chemical purity. These chemical analyses are not a simple process and must be conducted by a qualified analytical laboratory, preferably one with a good reputation for their work nationwide.
A number of years ago, we collected quartz from many different sites in the Ouachita Mountains and had the material analyzed by the U. S. Bureau of Standards. They chose the quartz from the Old Coleman pit, near Jessieville, AR, as the National Standard to which all other quartz is compared. There were several deposits that graded nearly as good for lascas quality as the Coleman pit. Lascas is presently produced in Arkansas, not from that site, but from a vein deposit in Saline County by one company.If I can be of further assistance to you, don't hesitate to ask. Mike H.
Q. Has any Amethyst ever been found in Arkansas? If not, why not or do you think the possibility might exist?
A. Yes, amethyst has been reported in two distinctive geological occurrences. At the Crater of Diamonds State Park in Pike County near Murfreesboro there are sparse amethyst veins that crosscut the diamond-bearing intrusion. Rarely are any pieces of quality recovered by collectors or tourists. When the Park personnel deep plow the diamond field with a bull dozer with a stinger on the back, there is always a chance they will bring some of this amethyst to the surface.
The amethyst from this location looks much like Brazilian amethyst in its crystal size and color. It formed in pockets in calcite veins so it may have either calcite or the impressions of the calcite crystals on the opposite side of the points or crystal terminations. The second location is in Saline County were drusy amethystine quartz veins cut across an altered talc-serpentine body. The crystals from this location are always small, stubby and form pale amethystine crusts on the serpentine host rock. At both locations small dark brown needles of goethite are often encapsulated in the amethyst.
Q. I am going to Mt. Ida and Hot Springs looking for Facet grade quartz. Where is the best place to go? Also is there any place to fined amethyst, of facet grade?
A. No place that I know of for facet grade amethyst in Arkansas. See above about amethyst in Arkansas. As to facet grade quartz, every dealer that handles quartz will have some, but I suggest contacting Sonny Stanley in Mount Ida for the most reasonable prices. It really depends on what size facet rough you need. Check the quartz dealer list elsewhere on this web site for additional information.
Q. Does all the irradiated Arkansas quartz come out that "black" color, or does some of it turn out light? I have a light colored cluster that I was told was natural, but I have also been told clusters are rare. My son's special interest is smoky quartz but we are still learning (the more I learn about quartz, the less I know). Since we did not pay a whole lot for this specimen we are really wondering.
A. It can be difficult to know for certain about the irradiated Arkansas black quartz. If the dealer you purchased the specimen from was honest with you, they would have told you up front that the piece was irradiated. But, barring that, there are a few tips you can look for on your specimen. Does it have good zoned phantoms? Few of the the irradiated specimens have phantoms. If it is light colored, does it have a peculiar yellow smoky color? Irradiated quartz that has set in the sun for several months to a year may fade to have this color.
Natural smoky tends to be smoky to the base, whereas irradiated tends to have a white crystal base next to the matrix rock. If so black you can not see through it and having good surface luster, then it is probably irradiated. The problem is that the naturally smoky crystal is also a product of irradiation, but in the ground by natural processes, not by man artificially.
Many years ago there was one major find of natural smoky quartz on the north shore of Lake Ouachita in Garland County. It had a good surface luster, multiple phantoms, and was a pleasing transparent smoke color. It also had pleasing elongated crystal habit. Just 3 to 4 years ago a find was made, also in Garland County at the Smoky Crystal Mine, of a single vein of gemmy smoky quartz. It also had good surface luster and a pleasing transparent smoke color, but the crystals did not display phantoms and were short and stubby in habit.
For years, around Magnet Cove in Hot Spring County, collectors have picked up natural smoky quartz associated with brookite, a titanium mineral. The smoky quartz from this area often forms elongate crystals, but rarely has good shiny luster. The crystals were etched after they formed so they usually have dull luster. Also, they tend to have very stairstepped sides. Most often they have a peculiar gray color instead of a dark black. Specimens from Magnet Cove are often sold or traded without much cleaning being done to them because most collectors do not know how to remove all the iron and clay matrix stains. But I do, so sometimes I can pick up some real bargains!!
Q. Are there any good books on quartz that aren't totally metaphysical? Or does most info have to be sorted out of more general books?
A. Yes, there are several books concerning quartz family minerals that are worth reading. Probably my favorite for general information about all types of quartz is titled Quartz Family Minerals by Dake (or Drake), Feener, and Wilson (?) and was published in 1936 (?). It is a small book, but packed with information. There was one US Geological Survey Bulletin, Engel, A. E. J., 1951, Quartz crystal deposits of western Arkansas: U. S. Geological Survey Bulletin 973-E, p. 173-260 that is loaded with information about the veins and deposits of Arkansas.
It contains a lot of information about the general geology of the crystal-bearing region, too. You need to look at used book stores and geology book dealers to get either of these now because they have been out of print for so long. Try Amazon.com or Ed Rogers Geoscience Literature or Geoscience books on the Internet! Search under Geology books or mineral books to find the major dealers.
Q. (1)I have found what I call "smoky" crystal points intermixed with clear crystal in several pockets at my mine (Sweet Surrender Crystal Mine). The mine is in a shale formation. The smoky points have a light golden cast and some have phantoms inside. What causes the smoky color and why would they randomly occur with the clear crystal? With appreciation, Stu Schmitt
A. I have not, unfortunately for me, visited this mine. However, the smoky color of smoky quartz is caused by natural radioactive materials having been present as some time during or after the formation of the crystal.
All crystals, quartz and otherwise are zoned internally, because the fluids they formed from changed during the crystallization process. Aluminum must be present in quartz in trace amounts for radiation to cause the smoky color. The aluminum is present as a rare substitute for silicon in the mineral's atomic structure. So if you have a crystal forming from hot water and the amount of silica and aluminum present in the water varies during the formation of the mineral, then radiation occurs, the crystal will contain smoky phantoms.
Be certain that the crystal is truly smoky and does not just contain gray or black phantoms, because that is an entirely different situation. Inclusions are often deposited on the surfaces of the crystals as they form so you see the shape of the earlier formed crystal inside mother nature's final creation.
Q. (2) In the same area where I found the smoky crystals, I found a large (2.5" diameter) broken point with a clump (3/4" x 1/2" x 1/8") of black stuff in it. It somewhat looks like petrified wood. Where can I get this analyzed and will it be expensive to do so?
A. Send a sample to my attention (Mike Howard), Arkansas Geological Commission, 3815 W. Roosevelt Road, Little Rock, AR 72204, and I will get our agency chemist to figure out what it is. No cost to you.
Q. When would be the best time to go crystal hunting?Trudy OK
A. Trudy in OK, I think the best time is in the spring or the fall when the weather is more cooperative -- cooler and less humid than summer, and less varmints around (like snakes, chiggers, and ticks). Late fall after the leaves are turning or off the trees or early spring before the leaves are real large on the vegetation makes it easier to see where you are going.
more Q&A about quartz on the next page
Ch 4, page 3
mailto:jmichaelhoward@sbcglobal.net revised July 1998
©Rockhounding Arkansas 1998 http://rockhoundingAR.com