square-cut anorthite - Japansquare-cut anorthite - Japan

Anorthite Value, Price, and Jewelry Information

The rarest plagioclase feldspar, anorthite is very rarely faceted.

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The rarest plagioclase feldspar, anorthite is very rarely faceted.

square-cut anorthite - Japan
Custom square-cut anorthite with copper inclusions, 0.23 cts, 3.6 mm, Miyake-jima, Japan. © The Gem Trader. Used with permission.

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Anorthite Value

anorthites - Italy
Anorthites on basalt, from the type locality, Mt. Somma-Vesuvius Complex, Napoli, Campania, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.

What is Anorthite?

Anorthite is the most calcium-rich/sodium-poor plagioclase feldspar (90-100% Ca/10-0% Na). It forms a solid solution series with sodium-rich/calcium-poor albite (90-100% Na/10-0% Ca). The other plagioclase stones — oligoclase, andesine, labradorite, and bytownite — have intermediate compositions.

Although anorthites occur in many locations throughout the world, in many rock types and environments, it's the rarest plagioclase. Its crystals are seldom transparent. As a result, anorthites cut into gemstones are an extremely rare sight.

Does Anorthite Make a Good Jewelry Stone?

Some plagioclases, like labradorite, make popular gemstones. Nevertheless, with a hardness of 6 to 6.5 and perfect cleavage in two directions and imperfect in another, anorthites are still susceptible to damage from scratches and blows against hard surfaces. As ring stones, anorthites would need protective settings. Use for earrings, pendants, and brooches would be more advisable.

Of course, you're more likely to find anorthites in a mineral collection than a jewelry collection.

Are There Synthetic Anorthites?

Scientists have synthesized anorthite crystals for mineralogical research. However, there's no known jewelry use for this material.

Where are Anorthites Found?

Notable sources include the following:

  • United States: Great Sitkin Island, Alaska; Pala, California; Italian Mountain, Colorado; Grass Valley, Nevada.
  • Finland; Greenland; India; Italy; Japan; Sicily; Sweden; United Kingdom.
anorthite crystals - Japan
Anorthites, partially coated with a film of blackish, glassy lava, Miyake-jima, Izu Archipelago, Tokyo Prefecture, Japan. © Rob Lavinsky, www.iRocks.com. Used with permission.

Stone Sizes

Rare, faceted gems are always small. However, a locality on Great Sitkin Island, Alaska has yielded cut gems as large as eight carats. This pale yellow anorthite may be the largest known.

How to Care for Anorthites

Due to their cleavage, avoid cleaning anorthites with mechanical cleaning systems, like steam and ultrasound. Clean them only with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more recommendations.

Joel E. Arem, Ph.D., FGA

Dr. Joel E. Arem has more than 60 years of experience in the world of gems and minerals. After obtaining his Ph.D. in Mineralogy from Harvard University, he has published numerous books that are still among the most widely used references and guidebooks on crystals, gems and minerals in the world.

Co-founder and President of numerous organizations, Dr. Arem has enjoyed a lifelong career in mineralogy and gemology. He has been a Smithsonian scientist and Curator, a consultant to many well-known companies and institutions, and a prolific author and speaker. Although his main activities have been as a gem cutter and dealer, his focus has always been education. joelarem.com

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