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What Is Mariposite?
“Mariposite” is an informal name that is most often used for green micas that are thought to be colored by small amounts of chromium. The name “mariposite” has also been used for a group of green and white metamorphic rocks that contain significant amounts of green mica. “Mariposite” has been used in many different contexts since the…
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Uses of Pegmatite
Pegmatite rock has very few uses. However, pegmatite deposits often contain gemstones, industrial minerals, and rare minerals. ARCHITECTURAL STONE Pegmatite rock has limited use as an architectural stone. Occasionally it is encountered in a dimension stone quarry that produces granite for architectural use. If the pegmatite is sound and attractive, it might be cut into slabs and polished…
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Rare Minerals in Large Crystals
In the early stages of crystallization, the ions that form high-temperature minerals are depleted from the melt. Rare ions that do not participate in the crystallization of common rock-forming minerals become concentrated in the melt and in the excluded water. These ions can form the rare minerals that are often found in pegmatites. Examples are small ions…
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Activity at the Margins of a Batholith
Pegmatites form from waters that separate from a magma in the late stages of crystallization; this activity often occurs in small pockets along the margins of a batholith. Pegmatite can also form in fractures that develop on the margins of the batholith. This is how “pegmatite dikes” are formed. Because these dikes and pockets are small in size,…
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The Rock with Large Crystals
Large crystals in igneous rocks are usually attributed to a slow rate of crystallization. However, with pegmatites, large crystals are attributed to low-viscosity fluids that allow ions to be very mobile. During the early states of a magma’s crystallization, the melt usually contains a significant amount of dissolved water and other volatiles such as chlorine,…
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What is Pegmatite?
Pegmatites are extreme igneous rocks that form during the final stage of a magma’s crystallization. They are extreme because they contain exceptionally large crystals and they sometimes contain minerals that are rarely found in other types of rocks. To be called a “pegmatite,” a rock should be composed almost entirely of crystals that are at least one centimeter in diameter. The…
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Other Uses of Obsidian
Freshly broken pieces of obsidian have a very high luster. Ancient people noticed that they could see a reflection in obsidian and used it as a mirror. Later, pieces of obsidian were ground flat and highly polished to improve their reflective abilities. Obsidian’s hardness of 5.5 makes it relatively easy to carve. Artists have used obsidian to…
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Uses of Obsidian in Jewelry
Obsidian is a popular gemstone. It is often cut into beads and cabochons or used to manufacture tumbled stones. Obsidian is sometimes faceted and polished into highly reflective beads. Some transparent specimens are faceted to produce interesting gems. The use of obsidian in jewelry can be limited by its durability. It has a hardness of about 5.5…
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Obsidian in Modern Surgery
Although using a rock as a cutting tool might sound like “stone age equipment,” obsidian continues to play an important role in modern surgery. Obsidian can be used to produce a cutting edge that is thinner and sharper than the best surgical steel. Today, thin blades of obsidian are placed in surgical scalpels used for…
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Stone Age Manufacturing and Trade
The manufacture of obsidian tools by humans dates back to the Stone Age. At some locations, tons of obsidian flakes reveal the presence of ancient “factories.” Some of these sites have enough waste debris to suggest that many people labored there for decades producing a variety of obsidian objects. Making arrowheads, spear points, knife blades,…