Articles

Articles

September / October 2004

Quartz
quartz cluster Rock crystal quartz, the most common gem variety of quartz crystal, is, like all quartz, formed from the two most abundant elements in the earth's crust: silicon and oxygen. For centuries early civilizations believed that these pinhead size to nearly a meter in diameter rock crystals were permanently frozen ice. Quartz's high thermo-conductivity, which makes it feel cool to the touch, may have added to this belief. Regardless of what early people may have believed, historical records show the use of rock crystal for decoration and jewelry for at least 4,000 years. Tools and weapons were made from rock crystal long before it was used for decoration and jewelry.

During the late 1980's and early 1990's, metaphysical uses and applications of rock crystal resulted in an increase in its production and processing. The metaphysical market used raw crystal in jewelry, person power and healing devices, and as charms. Additionally, spheres, sculls, pyramids, and other metaphysical objects were made from rock crystal. During the height of the trend, these uses accounted for 40% or more of the rock crystal consumed in the United States and also resulted in price increases for most of the crystals. Today, the metaphysical market has declined from its peak and appears to have stabilized at about 15% to 20% of total rock crystal consumption.

The market for rock crystal carvings, objects of art, and spheres is still strong. One piece of evidence of the demand for quality rock crystal for these types of uses is the level of sales of high quality quartz crystals from the National Defense Stockpile (NDS). During fiscal year 1994, sales of quartz crystals from the NDS totaled 313.1 metric tons valued at about $6.3 million, of this total; 96.8 metric tons valued at $3.21 million were sold during 6 days of the Tucson Gem and Mineral Show in February. During fiscal year 1993, NDS sold 176.8 metric tons of quartz valued at $1.64 million.

A gem dealer who purchased NDS quartz in Tucson shared the following information with the author: A 3,412 gram piece of quartz was purchased for about $120. The purchaser blocked out a totally flawless piece that was sent to a U.S. sphere cutting operation to be made into a flawless sphere. The sphere factory charged $48 to cut and polish a high-quality 84 millimeter, 844 gram sphere. The dealer sold the finished sphere for $1,200. This is only one dealers reported success in using NDS rock crystal and may not represent the outcome of any of the other NDS quartz sales.

Arkansas: To many in the gemstone industry, Arkansas and rock crystal quartz are synonymous. Mount Ida, Fisher Mountain, Hot Springs, and Jessieville names mean quartz crystals to many people, but in fact, they are towns or places in the Arkansas quartz belt. Not only is Arkansas the major producer of gemstone and decorative rock crystal but it is the only producer of "lascas” the feed material used to make synthetic quartz.

The rock crystals are produced from quartz veins in sandstones and shales of the central part of the Ouachita Mountains. The quartz belt is about 240 kilometers long and 24 kilometers wide, extending southwest from near Little Rock all the way to northern Oklahoma. The crystals are beautifully formed with lustrous faces; many have water clear, colorless terminations. Commonly, they are milky in appearance because of inclusions. On large plates of crystals the crystals are often short and stubby, but in smaller crystals it is not unusual for them to have a length that is at least 6 times their diameter. Many of these slender points are used as “gem points” in making earrings and pendants.

Historically, the demand for crystals was from tourists, collectors, interior decorators, carvers, sphere makers, and certain industrial and military applications. However, in recent years the increased use of quartz crystals in the metaphysical field has greatly impacted the demand and price for Arkansas quartz. Another market for the crystals is as feed material to be irradiated to produce smoky quartz. Most smoky quartz from Arkansas is not natural, but is irradiated rock crystal. Although it’s not the only U.S. producer of rock crystals, Arkansas is by far the largest; its quartz crystal mining industry is measured in millions of dollars per year.

California: Deposits in California are another source of significant amounts of quality rock crystal. For many years cobbles and round crystals have been found in streambeds in Amador and Calaveras Counties. The best quality, largest, and most abundant crystals come from ancient stream channels in the Mokelumne Hill area of Calveras County. Over the years, various mines in the area have produced thousands of kilograms of rock crystal, with some of the individual crystals weighing as much as 275 kilograms and many of the crystals measuring more than 600 millimeters in length and 250 millimeters in diameter. The American Museum of Natural History has a 150 millimeter sphere cut from a Mokelumne Hill rock crystal. Additionally, the pegmatites of Hiriart Hill, San Diego County, have produced hundreds of kilograms of fine-quality rock crystal from which a number of 60 to 90 millimeter spheres have been cut.

From the USGS website

Hardness and Specific Gravity
Hardness and specific gravity are two of the major characteristics of gemstones.
Hardness of a gemstone is its resistance to scratching and may be described relative to a standard scale of 10 minerals known as the Mohs scale. F. Mohs, an Austrian mineralogist, developed this scale in 1822.
According to Mohs' scale, the hardness of

Talc is 1	Feldspar is 6
Gypsum is 2	Quartz is 7
Calcite is 3	Topaz is 8
Fluorite is 4	Sapphire is 9
Apatite is 5	Diamond is 10

Specific gravity is the number of times heavier a gemstone of any volume is than an equal volume of water; in other words, it is the ratio of the density of the gemstone to the density of water.

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Minerals from Another World

Follow the lastest discoveries from NASA, as Mars Rovers Spirit and Opportunity continue to explore, experiment and send back images from Mars.Wouldn't you love a few of these rocks for your collection?
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Recent highlights:

11/4/04		Spirit Adds Clues About History of Rocks in Martian Hills Full Press Release Layers in 'Tetl': NASA's Mars Exploration Rover Spirit has examined the layered structure of this rock, called "Tetl," in the "Columbia Hills." This approximately true-color view was made from frames taken by Spirit's panoramic camera on the rover's 264th martian day....Read More
10/7/04		'Escher' Rock: This false-color image taken by NASA's Mars Exploration Rover Opportunity shows a rock dubbed "Escher" on the southwestern slopes of "Endurance Crater." Scientists believe the rock's fractures, which divide the surface into polygons, may have been formed by one of several processes...Read More
8/6/04		"Endurance Crater's" Dazzling Dunes: (false-color): As NASA's Mars Exploration Rover Opportunity creeps farther into "Endurance Crater," the dune field on the crater floor appears even more dramatic. This false-color image taken by the rover's panoramic camera shows that the dune crests have accumulated more dust than the flanks of the dunes and the flat surfaces between them. Read More
7/16/04		Chlorine Goes Deep: This image taken by the navigation camera on the Mars Exploration Rover Opportunity shows the layers of bedrock that line the walls of "Endurance Crater." Opportunity has been inching down the crater walls, investigating distinct layers of rock for clues to Mars' buried past. The various layers are labeled here as "A" through "F." Targets within these layers, including millstone, are also indicated.Read More
6/25/04		'Endurance' Tells Story of Mars' History: This false-color image shows the area inside "Endurance Crater" that the Mars Exploration Rover Opportunity has been examining. The rover is currently investigating the distinct layers of rock that make up this region. Each layer is defined by subtle color and texture variations and represents a separate chapter in Mars' history. Read More
6/15/04		'Tennessee' Clues: This false-color image shows the area within "Endurance Crater," currently being investigated by the Mars Exploration Rover Opportunity. The rover is inspecting a hole it drilled into a flat rock (center) dubbed "Tennessee," which scientists believe may be made up of the same evaporite-rich materials as those found in "Eagle Crater." Read More
6/15/04		Crater of Clues: This 360-degree panorama shows "Endurance Crater" and the surrounding plains of Meridiani Planum. This is the second large panoramic camera mosaic of Endurance, and was obtained from a high point near the crater's south rim. Read More Large Panoramic Image
6/2/04		The Colors of "Endurance": This false-color image shows visible mineral changes between the materials that make up the rim of the impact crater known as "Endurance." The image was taken by the panoramic camera on NASA's Mars Exploration Rover Opportunity using all 13 color filters. The cyan blue color denotes basalts, whereas the dark green color denotes a mixture of iron oxide and basaltic materials. Reds and yellows indicate dusty material containing sulfates. Read More
4/15/04		Mars Rover Finds Rock Resembling Meteorites That Fell to Earth: NASA's Opportunity rover has examined an odd volcanic rock on the plains of Mars' Meridiani Planum region with a composition unlike anything seen on Mars before, but scientists have found similarities to meteorites that fell to Earth. Read More
4/15/04		Smooth Side of 'Route 66': This image was taken by the microscopic imager onboard NASA's Mars Exploration Rover Spirit on sol 99 (April 13, 2004). It is a close-up look at a portion of the rock called "Route 66," which was brushed by the rover's rock abrasion tool. This image intrigues scientists because it looks very different from the microscopic images taken of other brushed rocks at the Gusev Crater location. Read More
4/1/04		Spirit Finds Multi-Layer Hints of Past Water at Mars' Gusev Site: Clues from a wind-scalloped volcanic rock on Mars investigated by NASA's Spirit rover suggest repeated possible exposures to water inside Gusev Crater, scientists said Thursday. Gusev is halfway around the planet from the Meridiani region where Spirit's twin, Opportunity, recently found evidence that water used to flow across the surface. Read More
3/23/04		Standing Body of Water Left Its Mark in Mars Rocks: NASA's Opportunity rover has demonstrated some rocks on Mars probably formed as deposits at the bottom of a body of gently flowing saltwater. "We think Opportunity is parked on what was once the shoreline of a salty sea on Mars," said Dr. Steve Squyres of Cornell University...Read More
3/18/04		Spirit's Destination (panorama): This panoramic image mosaic from the Mars Exploration Rover Spirit panoramic camera, shows the rover's destination toward the hills nicknamed the "Columbia Hills," on the right. The rover's heatshield can be seen on the left as a tiny bright dot in the distance, just under the horizon. Dark drift material can be seen in the image center. Read More Large Panoramic Image
3/18/04		Mineral in Mars 'Berries' Adds to Water Story: A major ingredient in small mineral spheres analyzed by NASA's Mars Exploration Rover Opportunity furthers understanding of past water at Opportunity's landing site and points to a way of determining whether the vast plains surrounding the site also have a wet history. Read More
3/18/04		A Bowl of Hematite-Rich 'Berries': This graph shows two spectra, or light signatures, of outcrop regions near the Mars Exploration Rover Opportunity's landing site. The blue line shows data for a region dubbed "Berry Bowl," which contains a handful of the sphere-like grains dubbed "blueberries." Read More
3/2/04		The Texture of El Capitan: This image, taken by the panoramic camera on the Mars Exploration Rover Opportunity, shows a close up of the rock dubbed "El Capitan," located in the rock outcrop at Meridiani Planum, Mars. This image shows fine, parallel lamination in the upper area of the rock, which also contains scattered sphere-shaped objects ranging from 1 to 2 millimeters (.04 to .08 inches) in size. Read More
3/11/04		The Minerals at 'El Capitan': The white curve in this image shows the spectrum, or light signature, of a region of rock outcrop dubbed "El Capitan" near the Mars Exploration Rover Opportunity's landing site. The data were taken by rover's miniature thermal emission spectrometer instrument, located on its panoramic camera mast assembly. Read More
3/2/04		Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet: Scientists have concluded the part of Mars that NASA's Opportunity rover is exploring was soaking wet in the past. Evidence the rover found in a rock outcrop led scientists to the conclusion. Clues from the rocks' composition, such as the presence of sulfates, and the rocks' physical appearance, such as niches where crystals grew, helped make the case for a watery history. Read More
3/2/04		Mineral Tells Tale of Watery Past: This spectrum, taken by the Mars Exploration Rover Opportunity's Moessbauer spectrometer, shows the presence of an iron-bearing mineral called jarosite in the collection of rocks dubbed "El Capitan." "El Capitan" is located within the rock outcrop that lines the inner edge of the small crater where Opportunity landed. The pair of yellow peaks specifically indicates a jarosite phase, which contains water in the form of hydroxyl as a part of its structure. Read More
2/20/04		Plotting and Scheming: This graphic is a planning tool used by Mars Exploration Rover engineers to plot and scheme the perfect location to place the rock abrasion tool on the rock collection dubbed "El Capitan" near Opportunity's landing site. "El Capitan" is located within a larger outcrop nicknamed "Opportunity Ledge." Read More
2/19/04		Opportunity Examines Trench As Spirit Prepares To Dig One: By inspecting the sides and floor of a hole it dug on Mars, NASA's Opportunity rover is finding some things it did not see beforehand, including round pebbles that are shiny and soil so fine-grained that the rover's microscope can't make out individual particles. Read More
2/13/04		Flaky "Mimi": This color image taken by the Mars Exploration Rover Spirit's panoramic camera on Sol 40 is centered on an unusually flaky rock called Mimi. Mimi is only one of many features in the area known as "Stone Council," but looks very different from any rock that scientists have seen at the Gusev crater site so far. Read More
2/9/04		Mars Rock Formation Poses Mystery: This sharp, close-up image taken by the microscopic imager on the Mars Exploration Rover Opportunity's instrument deployment device, or "arm," shows a rock target dubbed "Robert E," located on the rock outcrop at Meridiani Planum, Mars. Read More
2/4/04		Thar be Hematite!: This map of a portion of the small crater currently encircling the Mars Exploration Rover Opportunity shows where crystalline hematite resides. Red and orange patches indicate high levels of the iron-bearing mineral, while blue and green denote low levels. Read More The Lure of Hematite ~ NASA Science 3/28/01 Why Hematite? ~ NASA 2/14/04
2/4/04		Mars Under the Microscope: This magnified look at the martian soil near the Mars Exploration Rover Opportunity's landing site, Meridiani Planum, shows coarse grains sprinkled over a fine layer of sand. Read More..
1/28/04		A Geologist's Treasure Trove: This high-resolution image captured by the Mars Exploration Rover Opportunity's panoramic camera highlights the puzzling rock outcropping that scientists are eagerly planning to investigate. Presently, Opportunity is on its lander facing northeast; the outcropping lies to the northwest. Read More Large Panoramic Image
1/20/04		The Mystery Soil: This high-resolution image from the panoramic camera on the Mars Exploration Rover Spirit shows the region containing the patch of soil scientists examined at Gusev Crater just after Spirit rolled off the Columbia Memorial Station. Scientists examined this patch on the 13th and 15th martian days, or sols, of Spirit's journey. Read More
1/13/04		In the Far East: In the distance stand the east hills, which are closest to the Mars Exploration Rover Spirit in comparison to other hill ranges seen on the martian horizon. The top of the east hills are approximately 2 to 3 kilometers (1 to 2 miles) away from the rover's approximate location. This image was taken on Mars by the rover's panoramic camera. Read More Large Panoramic Image
1/12/04		Mars in Full View: This is a medium-resolution version of the first 360-degree panoramic view of the martian surface, taken on Mars by the Mars Exploration Rover Spirit's panoramic camera. Part of the spacecraft can be seen in the lower corner regions. Read More Large Panoramic Image