The trails around Crystal Bridges are open from dawn to dusk. Please respect these hours and all posted guidelines when claiming this Earthcache.
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Permission to publish this cache granted by Crystal Bridges Museum of American Art.
QUARTZ:
Quartz is one of the most abundant minerals in the Earth’s crust and the most abundant mineral found at the Earth’s surface. Quartz is composed of silicon and oxygen and is common throughout the world, although most of it is not crystallized. Crystallization occurs when the silicon dioxide or silica is heated. The source of the heat can be extremely hot water from underground sources, which fills open fissures to create filled quartz veins. During the cooling, the silicon and the oxygen recombine as molecules formed by one silicon atom and four oxygen atoms. All of the crystals have six sides or prism faces because of their molecular structure. Quartz is rated seven on the Mohs hardness scale; diamonds are rated ten. (source: Encyclopediaofarkansas.net)
Only a very small percentage of quartz is found in the form of the iconic, clear individual points, which is known as "rock crystal."
Quartz forms at all temperatures and is abundant in igneous, metamorphic and sedimentary rocks. It is highly resistant to both mechanical and chemical weathering. This durability makes it the dominant mineral of mountaintops and the primary constituent of beach, river, and desert sand. One of the first uses of quartz, in the form of flint, was in the production of objects such as knife points and arrowheads. One such arrowhead, dating back an estimated 11,000 years, has been found in Garland County, AR.
Quartz is one of several minerals which are piezoelectric, meaning that when pressure is applied to quartz, a positive electrical charge is created at one end of the crystal and a negative charge is created at the other. It is also strongly pyroelectric which means that temperature changes can cause the development of positive and negative charges within the crystal. These properties make quartz valuable in electronics applications. Due to issues of purity and consistency, natural quartz has yielded to manufactured quartz in most commercial applications. Electronics-grade manufactured quartz is used as a component in consumer electronics such as computers, cell phones, radios and TVs.
Classification:
Today, quartz is generally classified based on visual appearance and the ability to see its structural formation under a microscope. There are two primary classifications, noted in the chart below:
Macro- and cryptocrystalline forms of quartz differ in the way they grow.
- Macrocrystalline quartz grows by adding molecules to the crystal's surface, layer by layer.
- Cryptocrystalline quartz forms from a colloidal watery solution of silica
QUARTZ IN ARKANSAS:
Arkansas is one of a small number of places in the world with enough quartz crystals to justify commercial mining. The crystals in the dominant belt (centered around Mount Ida, Arkansas) are estimated to have formed about 280 to 245 million years ago. Though the amount of unmined quartz in the state is not yet known, Arkansas does have, in terms of both size and quality, some world-class deposits of quartz. In 1967, the General Assembly adopted the quartz crystal as the Arkansas State Mineral. (source: Encyclopediaofarkansas.net)
QUARTZITE:
In addition to the crystal points on display, you can also examine fine examples of quartzite. The quartzite rocks are those hosting the crystals - they are surrounded by native sandstone boulders.
Quartzite is a hard metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating ad pressure usually related to tectonic compression. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide.
When sandstone is cemented to quartzite, the individual quartz grains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals. Most or all of the original texture of the sandstone is erased and the grainy, sandpaper-like surface becomes glassy in appearance. (source: Wikipedia.org)
Quartzite shares the hardness properties of quartz, ranking at 7 of 10 on the Mohs hardness scale. This is one rock that you don't want to strike with a hammer unless you are wearing protective eyewear and clothing - a hammer strike will most likely bounce off, and will frequently produce sharp flakes and even sparks.
To log this cache, please send answers to the following questions via the Messaging or Email features on my account.
1. According to the sign near the display, from what town did this quartz and quartzite come?
2. What is the approximate size of the largest crystal point you can find here? Are these crystals a) Macrocrystalline, or b) Cryptocrystalline?
3. What color is the quartzite rock here, and why?