Tourmaline refers to an extensive collection of boron silicate minerals. Although they share the same crystal structure and physical properties, these minerals have vastly different chemical compositions. Tourmaline is a mineral found in more color combinations and designs than any other group due to its wide range of color zoning and pieces.
Natural tourmaline beads, one of the most loved gemstones in the world, is a birthstone for October. Tourmaline is very easy to find in jewelry shops due to its popularity. Mineral specimen collectors also value well-formed tourmaline crystals. Collectors can make thousands of dollars selling specimens with attractive crystal forms and colors.
Geologic Occurrences of Tourmaline
Tourmaline is commonly found as an accessory mineral in metamorphic and igneous. Tourmaline crystals can be large and well-formed, mainly if formed in fractures or cavities during hydrothermal activity. Tourmaline is a strong and resilient mineral. This allows it to survive stream and beach transport and can be found as durable grains in sediments or sedimentary rocks.
Tourmaline Crystals
Hydrothermal activity is responsible for forming some of the most stunning tourmaline crystals. These crystals are formed when hot water and vapors transport the elements required to form tourmaline. They include pockets, voids, and fractures that allow for crystal growth. These cavities contain tourmaline crystals that range from tiny crystals of millimeter size to large prisms that weigh over 100 kg.
As an accessory mineral, tourmaline.
Tourmaline is most commonly found as an accessory mineral in metamorphic and igneous rocks. It is often found as tiny millimeter-sized crystals scattered throughout granite, pegmatite, or geodes. This mode of occurrence means that tourmaline is only a small percentage of the rock’s total volume. Black school is the most common form of tourmaline used as an accessory mineral.
Tourmaline Sources
Brazil is the world’s largest source of tourmaline. It has been around for almost 500 years. Portuguese explorers discovered green and blue tourmaline in the 1500s from native peoples and by panning streams for gold. These colorful stones were thought to be emeralds or sapphires. They were sent back to Portugal to be cut into gems and made jewelry for the rich and royalty. (Tourmaline wasn’t recognized until 1793 as a distinct mineral.
Since the late 1800s, tourmaline has been discovered in the pegmatite deposit of Minas Gerais in Brazil. Millions of carats have been made of tourmaline in many colors, including some bicolor. This variety of Brazilian tourmaline has been the primary source of the world’s gem and jewelry markets.
After the 1821 discovery and exploration of tourmaline in the vicinity of Paris, Maine, the first commercially viable gemstone mine was established in the United States. Numerous Maine locales have produced significant quantities of pink and green tourmaline over the past 200 years.
The tourmaline mines in southern California are the most crucial source of tourmaline in America. There has been tourmaline mining since the late 1800s. Tourmaline is California’s most valuable gem material based on its cumulative dollar value. This production occurred in Riverside and San Diego Counties over 100 years ago. There were tons of red tourmaline mined and sent to China, where it was used to produce snuff bottles and carvings, jewelry, and other products. A little tourmaline can be made today by small-scale mining. Today, miners sell most of the best-quality production as mineral specimens.
Physical Properties of Tourmaline
There are a few properties in tourmaline that can help you identify it. Identification should be simple if you have a crystal of tourmaline.
- Tourmaline is a prismatic crystal habit with apparent striations paralleling the long axis.
- Many tourmaline crystals have rounded edges and triangular cross-sections.
- Color-zoned tourmaline crystals can be found along their length or cross-sections.
- Pleochroic Tourmaline is possible with the darkest colors viewing down the C axis and lighter colors viewing perpendicularly to the C axis.
If you suspect that tourmaline may be an accessory mineral within an igneous, metamorphic rock, don’t worry. These rocks often contain tiny crystals called multicolored tourmalines. Use a hand lens to look for striations or rounded cross-sections.
Tourmaline is known for its indistinct cleavage. Any specimen that has apparent separation will most likely not be tourmaline. It might not be helpful to use color. Black is the most common color for tourmaline, but it can also be found in other colors.
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