The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Feldspar|
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.
Andesine is named after the Andes Mountains of South America.
Andesine is known from many localities, including California; Utah; Colorado; South Dakota; Minnesota; New York; North Carolina; Colombia; Argentina; Greenland; Norway; France; Italy; GermanY; South Africa; India; and Japan.