Long Articles

Chemistry in Mining

During Earth Science WeekTM, we went to a lecture by Dr. Innocent Pumure from UCM called “Sonochemical Extraction of Arsenic and Selenium from Pulverized Rocks Associated with Mountaintop Removal Valley Fill (MTR/VF) Method of Coal Mining”.

You may be wondering, what is Mountaintop Removal Valley Fill Mining? First, the excavation company blows up (or strips) the top part of the mountain to remove vegetation and expose the coal seams. The coal seams are then mined through the open cast/strip method, and the extra rock and soil is dumped in nearby valleys called valley fills. It is cheaper and easier to do than regular mining, where they dig a vertical shaft down and do everything through the tunnel, but it blasts the mountain apart and looks ugly. Since 30% of electricity in the USA comes from coal, valley fill mining is still pretty popular.

In 2002, the EPA found too much selenium downstream of a certain mine in West Virginia (we’re not going to say which one). It was over 5 ng/mL, which was the limit back then.[*] 7 years later, there was still an active mine there and the water still had too much selenium. Even worse, the surrounding sediment had 10.7 mg/kg selenium. This could cause problems for the environment later. Due to bioaccumulation, you could say once it’s in there, it’s really in there.

So now we get to the topic of Dr. Pumure’s talk, in which he and his colleagues discovered a way to quickly find out how much selenium and arsenic were in the ground around this mine in West Virginia. When you do a chemical analysis, you usually have to break down the samples in order to measure what is in them. One method to do this would be to take some core samples and do an acid extraction, but that takes a long time and uses a lot of reagents. Sonochemical extraction uses ultrasound energy to accelerate the leaching process that would naturally happen as rocks become weathered. Since it is ultrasound, it does not directly touch the sample, is minimally invasive, and does not need any reagents except water.

Next, he explained the methodology, which means a description of exactly how they did it in the lab: the size of the extraction cells, how much water and power were used (200W/cm3), how long the samples were sonicated, and all the other pertinent information for chemists. Pumure actually spent quite a lot of time finding out the optimal sonicating time to get the best extraction. It turned out the best times for his sample sizes were 20 minutes for Se and 25 minutes for As. That’s really fast![**] Then, he did a comparison to a chemical sequential extraction to make sure that the sonochemical extraction method was getting everything. To summarize, yes it was. Finally, he did a principal component analysis of core samples from different places all over the mountain using this same technique. They found some really interesting trends and correlations, for example, it appears that there is more arsenic in illite clay than other types of clay.

This research has many useful applications. If you were running a mine, you could take samples more frequently to see if your mine is polluting the surrounding environment, and then you could do something about it before the EPA finds out. The method could probably be used for other analytes, too. For other research needs, you could now quickly analyze large batches of mineral samples to get lots of data that would otherwise be too expensive or time consuming to obtain.

[*]The EPA has since lowered the limit and now it is 3.1 ng/mL.
[**]For comparison, some of my colleagues do chemical extractions that take 2 days.
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Mozarkite Trip to Lincoln

MOZARKITE, MISSOURI’S STATE STONE by Roger K. Pabian

(Editor’s note: This article was written by Roger and printed in The Gemrock in 2002. It is written about a field trip taken by Roger and Bill and Betty White.)

On May 3, I took a trip to Kansas City and then on to Lincoln, Missouri, to examine the in place occurrence of Mozarkite, the Official State Gemstone of Missouri. As part of my ongoing study of cryptocrystalline and amorphous quartz family gemstones, I thought that the Mozarkite mine would be a worthwhile trip.

In Kansas City, I joined up with Bill and Betty White on Friday afternoon. Bill and I spent much of the afternoon at one of the major tool houses there and I purchased quite a few diamond tools and other tools that would be of use for stone and metal work. We also hit one of the retail salvage outlets, a store that carries distressed merchandise, as they often have many tools of considerable value for very low prices.

On Saturday morning about 7:00 A.M. we left Independence for the small town of Lincoln, Missouri. The town is famous for its annual rock swap in September. There we teamed up with Linville Harms, owner of the Mozarkite mine, and then went on to the mine. The attached photos of the Mozarkite and the Mozarkite mines help you get a better idea of what the site is like.

mozarkite

Photos by Roger K. Pabian

Mozarkite is not an accepted mineral name but is simply a trade name that was developed to promote the acceptance of the stone as Missouri’s official State Gem and to generate sales to both lapidary and tourists. The name has found acceptance in some circles but is not an acceptable mineral name in others.

Mozarkite has formed in place in marine sedimentary rocks of Ordovician age — it probably is most common in the Jefferson City Formation. The Jefferson City Formation is comprised mostly of dolomite with silty and cherty stringers running through it. There are very few fossils in dolomized rocks as the addition of magnesium to the calcium carbonate of the limestone usually results in complete re-crystallization of the rock and destruction of any fossils or sedimentary structures therein. We did observe a fragment of a brachiopod shell that escaped destruction. It appeared to be a flat-shelled, long-hinge lined form, probably a strophomenoid, but no other determination could be made of it. Much of the local lore about Mozarkite attributes it to igneous activity but there is no evidence for any in that area of Ordovician or younger rocks.

The Mozarkite appears to be of strictly marine sedimentary origin. Some of the nodules show evidence of an accumulation of siliceous gel or ooze on their outer surfaces.

There appears to be three different facies of Mozarkite. The gemmy kind is a dense, brittle form that shows no crystallinity at 10X magnification. A second kind is what the locals call “sugary” Mozarkite. Some of this is quite colorful and has interesting patterns and enjoys some gem use. The “sugary” kind, However, this does not polish nearly as well as the dense, brittle kind. Then, there are some nodules that appear to be very fine sandy textured.

The three facies or textures of Mozarkite suggest that sorting of particles may have been one of the key factors in the origin of the material. Sorting of particles simply means that as some energy form such as wind or flowing water moved a mixture of unconsolidated particles, the heaviest or largest particles are the first ones to drop out of suspension. You can observe this phenomenon on the gravel bars of a stream or in the bars along beaches, estuaries, or lagoons. The coarsest particles will be on the upstream end of the bar or nearer the bottom of the bar. It may well be that the gem Mozarkite is a quartz argillite, a sedimentary rock made up of quartz particles of clay size, that is, smaller than 1/256th of a millimeter. The gemmy facies could also be derived from silica of organic or volcanic origin. The “sugary” facies is made up of the particles larger than 1/16th but smaller than 1/4 mm.

The source for the silica that makes up Mozarkite is currently not known. It may have been from Precambrian granite rocks that are found to the south and east. Sponge spicules may have been the source of silica; I will not totally disregard them. However, I usually favored volcanic ash as the source of siliva for large bodies of chert or flint in marine sedimentary sequences. If there was any volcanic activity involved with Mozarkite, it was from volcanoes that were far away from the Mozarkite-bearing strata.

Mozarkite is a very interesting gem material that could shed a lot of light on the geologic events and processes that led to its formation. My comments above are only a few ideas about its occurrence. Like many other ideas on his stone, my hypotheses need more documentation before they can either be accepted or rejected. My hypotheses should probably read as follows: “Mozarkite is a quartz argillite of marine sedimentary origin that formed in situ in shallow seas of Ordovician age. The source of the quartz is shield rocks of Precambrian ages that lie to the southeast of the area from which it is not found.”

To prove that, several things need to be done. First, properly oriented (top and north) nodules need to be collected from in place in the mine pits. The nodules should not be examined in the field to avoid “high grading” the material. An outcrops map or diagram would need to be made that shows the places from which each nodule was taken. Similar sampling should be carried out from several different layers in several different parts of the mine. The facies of each nodule would need to be located on the map. Does one zone produce only sandy material whereas another produces only gemmy material? Or do these facies occur at random? Thin sections (30 microns) would have to be made. The nature of the particles (angular or rounded) and any cement between them would need to be noted. Is there a silica cement between the particles or does their angularity hold them together? Then other occurrences, both geographic and stratigraphic, of Mozarkite would have to be noted. The sedimentary structures in the Mozarkite and the host rock would also have to be observed and recorded.

By the time all of this is done, one has done enough work to earn a Master of Science Degree. As you see, there is no easy answer for Mozarkite. Perhaps, as a club, or group of clubs, we might think of funding a student to carry out the above kind of research.

mozarkite open pit mine Lincoln Sedalia

Linville Harms (left) of Sedalia, Missouri, and Bill & Betty White examine the open pit mine. Linville is the mine owner. Photo by Roger K. Pabian

 

Spring 2017 Lectures

Lectures presented by the Association of Earth Science Clubs of Greater Kansas City

Friday, March 10, 2017

3:00 p.m. “Opal Down Under”, Ron Wooly, Owner of Dreaming Down Under

Saturday, March 11, 2017

1:00 p.m. “Earth Science… Facts, Frauds and Scams”, Mark Sherwood, Independence Gem and Mineral Society

2:00 p.m. “The Life and Hard Times of the KU T. rex”, Dr. David Burnham, Research Associate, University of Kansas, Lawrence, Kansas

3:00 p.m. “Medullary bone in Tyrannosaurs: a question of chickens, eggs and possibly more”, Dr. Josh Schmerge, University of Kansas, Lawrence, Kansas

4:00 p.m. “History of Gold Mining”, Doug Foster, Show-Me Gold, Missouri

Sunday, March 12, 2017

2:00 p.m. “The Life and Hard Times of the KU T-rex”, Dr. David Burnham, Research Associate, University of Kansas, Lawrence, Kansas

3:00 p.m. “Islands in the sun: Eocene fossil mammals from Turkey”, Dr. Chris Beard, University of Kansas, Lawrence, Kansas

Special Exhibits 2017

KANSAS CITY GEM SHOW SPRING 2017 FEATURE EXHIBIT

ROCK ART –Stone Quilt Design; Susan Judy; Denver, CO and WKP Accent Tables; Bill Peterson; Boulder, CO
Colorado artists Judy and Bill have brought some of their creations to the Kansas City Show.  Judy inlays natural materials in a stone mosaic to create pictures and Bill uses natural materials to create tables.

INVITATIONAL EXHIBITS (more…)

How Amethyst Cathedrals are Formed

purple amethyst cathedral in a museum with other minerals

Amethyst cathedral at the Sutton Museum. Photo by Stephanie Reed

Article by Dr. Bill Cordua, University of Wisconsin-River Falls

Have you ever been to a show and seen enormous amethyst geodes or crystals 3-5 feet or more in height? The tubular geodes are lined with deep purple gemmy amethyst crystals. How do such wonders form?

These excellent geodes come from a region along the Brazil-Uruguay border. The genesis of deposits on the Brazil side of the border has recently been extensively researched by an international team of geochemists lead by H. Albert Gilg of Techniche University Munchen in Germany (Gilg, et. al., 2003). The geodes are mined from several lava flows belonging to the Parana Continental Flood Basalt Province. This was one of the largest outpourings of basalt lava known. An estimated 800,000 cubic kilometers of lava extruded over an 11 million year time span. For comparison, this would be enough to cover Minnesota with a pile of basalt lava over 2 miles high. The lava outburst occurred as part of the opening of the South Atlantic Ocean during Cretaceous time about 130 million years ago. Of all these flows, however, only a few are known to host amethyst cathedral geodes.

Gilg et al. proposed a 2-stage model for their formation. In the first stage the large hollows form. This was caused as volcanic gases were released from certain lavas as they cooled. Not every lava has enough dissolved gas to form such big openings. As gas bubbles emerged from the congealing lava (much as bubbles emerge when beer or soda pop is poured) they coalesced as they rose. The lava was cooling fast too, and soon became so thick and sticky that bubbles quite rising and were trapped. The bulbous to tubular shapes thus point towards the top of the flow, a fact easily seen when the geodes are in place in the mines. These cavities, though, were empty of crystals.

The second stage was the formation of the amethyst, plus celadonite, calcite and gypsum fillings. An important clue to this event is the presence of small gas and liquid bubbles (called fluid inclusions) trapped within these minerals. These are samples of the mineral-forming liquids caught as the crystals grew. Fluid inclusions are treasure troves of information when studied with sophisticated instruments. Analyses of the fluid inclusions in the amethyst, calcite and gypsum show them to be filled with slightly salty water. This water had a temperature of no more than 100 degrees C, and possible less than 50 degrees C, during mineral formation. These cannot be fluids related to the magma that formed the lavas.

What was the source of these fluids? An amazing story unfolds from the radiometric dating of the minerals. The basalts formed about 130 million years ago, but the green celadonite, which makes up the rinds of the geodes, formed about 70 million years ago. For 60 million years these enormous cavities sat empty of crystals. Trace element data from the fluid inclusions gives another important clue to the source of the mineral-forming fluid. Below the lavas is a large aquifer (the Botucatu aquifer) filled with ground water that closely resembles the fluid inclusion liquids. Uplift and tilting of the area about 70 million years ago would force water out of the aquifer into the porous areas of the overlying lava. In the lava flow these waters would have found volcanic glass. Glass breaks down over geologic time and makes silica and other chemicals available in a form that is readily soluble in water soaking through the rocks. The water carried these chemicals into the cavities, where the amethyst and other minerals grew due to cooling and pressure release.

The special combination of geologic circumstances, unfolding over millions of years, is not often duplicated. Understanding the process gives geologist tools to prospect more efficiently for these wonders.

Reference:
Gilg, H. et. al, 2003, “Genesis of amethyst geodes in basaltic rocks of the Serra Geral Formation (Ametista do Sul, Rio Grande do Sul, Brazil): a fluid inclusion, REE, oxygen, carbon, and Sr isotope study on basalt, quartz and calcite” Mineralium Deposita vol. 38, p. 1009-1025.

The Glacial Drifter 08/2011, The Gemrock 06/2015

Weathering

Weathering is when rocks break down in place, that is, without moving the rock. This is usually done by water, but there are plenty of other physical and chemical processes that break down rocks without moving them. Physical weathering occurs when a tree root grows into a rock and breaks through, when a river cuts through a canyon, when particles carried by the wind abrade the rock, or during the process of frost wedging, which is when water fills a crack in a rock and freezes, then the ice expands and makes the crack deeper. Chemical weathering can be caused by acid rain or even regular rain, as minerals in the water weaken the rocks and make it easier for them to be eroded or broken later. Minerals can even react with chemicals in the air (such as iron and oxygen reacting to form rust, also known as iron oxide) or with other minerals nearby. Minerals are made of chemicals, after all, and there is nothing stopping them from reacting with one another.

There are a lot of interesting ways that minerals can change due to weathering, both physical and chemical. For example:

  • Limestone dissolves
  • Calcite dissolves
  • Gold may dissolve if manganese is present
  • Silver minerals can change to horn silver (cerargyrite) or dissolve
  • Feldspar changes to clay
  • Olivine and hornblende change to serpentine or chlorite
  • Pyrite changes to limonite and hematite
  • Rhodochrosite and rhodonite change to psilomelane or pyrolusite (manganese) minerals
  • Copper sulfide minerals change to malachite, azurite, cuprite, or metallic copper, or may dissolve entirely
  • Some copper minerals become partly limonite

Adapted from an article in Cycad, Flint Chips, Osage Hills Gems 11/1992

Characterization of Green Amber

silver ring with oval green amber

Green amber ring owned by Stephanie. It has nothing to do with this article. Photo by Stephanie Reed

David highly recommends this article on green amber from Gems & Gemology, 2009. Here is the abstract.

Ahmadjan Abduriyim, Hideaki Kimura, Yukihiro Yokoyama, Hiroyuki Nakazono, Masao Wakatsuki, Tadashi Shimizu, Masataka Tansho, and Shinobu Ohki

Abstract: A peridot-like bright greenish yellow to green gem material called “green amber” has recently appeared in the gem market. It is produced by treating natural resin (amber or copal) with heat and pressure in two stages in an autoclave. Differences in molecular structure between untreated amber and copal as compared to treated “green amber” were studied by FTIR and 13C NMR spectroscopy, using powdered samples. Regardless of the starting material, the FTIR spectrum of “green amber” showed an amber pattern but with a characteristic small absorption feature at 820 cm-1. Solid-state 13C NMR spectroscopy of the treated material indicated a significantly lower volatile component than in the untreated natural resin, evidence that the treatment can actually “artificially age” copal. A new absorption observed near 179 ppm in the NMR spectra of all the treated samples also separated them from their natural-color counterparts.

To read the whole article, go here http://www.gia.edu/gems-gemology/fall-2009-green-amber-abduriyim and click on “Download PDF”.

How To Clean Rocks

Household Products That Can Be Used As Rock Cleaners

by Betsy Martin
Safety: Always use plastic containers, rubber or nitrile gloves, eye protection, good ventilation, and great care when handling these products.
1. Zud or Barkeeper’s Friend cleansers (contains oxalic acid) – Warm or hot solutions will remove iron stains and are helpful with clay deposits. These cleaners can be used with a toothbrush on sturdy surfaces.
2. Toilet Cleaner (the hydrochloric acid type) dissolves calcite rapidly. After treating anything with an acid, rinse very carefully and soak in ample fresh or distilled water for a while to leach out any acid remaining in crystal seams and fractures. You can then follow up with a final soak in dilute Windex to neutralize remaining traces of acid.
3. Lime Away (dilute hydrochloric acid) dissolves calcite more slowly. Rinse as you would for other acid treatments (see above).
4. Calgon – Dissolve this powdered water softener in water. Use for clay removal.
5. Vinegar (Acetic acid), soda water, colas (carbonic and phosphoric acids) – Will slowly etch out very delicate fossils in limestone. Rinse as you would for other acids (see above)
6. Iron Out (iron stain and clay remover) – Mix with warm water and use with good ventilation. It will lose strength if stored. Rinse with plain water.
7. Bleach – Dilute solutions of bleach can remove organic deposits and disinfect minerals collected in areas used by livestock. Rinse with plain water.
8. Hydrogen peroxide – Use to remove manganese stains. Rinse with plain water.
9. Citric acid – Use to remove manganese stains. Rinse as above for acids.
10. Windex (with ammonia) – A good clay deposit remover and final surface cleanup. Works well in ultrasonic cleaners. Rinse with plain water.
11. Distilled Water – Use to clean sensitive species and as a final soak after acid treatment.

Removing Thin Coatings:
On moderately hard minerals – use toothpaste (a feldspar abrasive) and a toothbrush.
On hard minerals – use toothbrush with pumice powder and water.
On calcite (including bruised places) – quickly dip in vinegar or Lime Away and rinse thoroughly. Repeat. Soak in plain water afterwards to leach any acid from cracks.

The following tools can be used for cleaning minerals and tools:
Toothpicks, seam ripper, bamboo sticks, sewing needles in a pin vise, old dental tools, old toothbrushes, periodontal brushes, canned air, Exacto knife, single edge razor blades, cheap small stiff bristle brushes.
Source: The Gemrock, 06/2015

Chemical Composition of Gemstones

Here’s a neat infographic from Compound Interest (one of my favorite websites) that describes 16 different gemstones and why they have different colors. It also includes their chemical formulas and hardness on the Mohs scale.

Many gemstones would be colorless or a different color if not for the presence of small amounts of transition metals such as chromium or titanium. For example, you can see that aquamarine and emerald both have the same chemical formula Be3Al2(SiO3)6, but emeralds are green because of chromium ions replacing some of the aluminum ions and aquamarines are blue because of iron 2+ or 3+ ions replacing some of the aluminum ions. Click through to read the whole article, because there are many other ways that gems and minerals get their colors!