Oligoclase Value, Price, and Jewelry Information

Comments

These feldspars are rarely encountered in gem form. Their occurrence is widespread throughout the world, in a great variety of rock types and environments, but in most cases transparent crystals are rare.

In many cases faceted gems are identified as a feldspar in the plagioclase series, but the finder does not have the instrumentation needed to pin down the species. This is accomplished by a combination of optical and X-ray analysis. A few plagioclase gems have been well characterized, however, and reported in the literature.

Name

Oligoclase comes from Greek words meaning little break because the cleavage was believed to be less perfect than in albite.

Occurrence

Oligoclase is reported from the Hawk Mine, Bakersville, North Carolina, in colorless to pale green facetable crystals. The indices are 1.537-1.547; density 2.651. Oligoclase is also reported from Kenya, colorless grains, with indices as follows: a = 1.538-1.540,= 1.542-1.544,  = 1.549- 1.550; birefringence 0.010-0.011; S.G. 2.64. North Carolina gems up to about 1-5 carats, colorless to pale green, are reported. Oligoclase from Baffin Island, N.W.T., Canada has yielded cut gems up to about 5 carats.

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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