Antieke juwelen glossarium
(verklarende woordenlijst)

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Feldspar

A large group of minerals that is found in a wide area of the earth, but only a few of its members are suitable for gemstones.

Feldspars are divided into several series:

• orthoclase (embracing moonstone and adularia) and microcline (embracing amazonstone)
• plagioclase (embracing sunstone, aventurine, feldspar, labradorite, and peristerite)
• celsian; each with several intermediate series

The group has also been called 'feldspath' but now is generally called 'feldspar'. The names of varieties refer to the nature of the Cleavage ('clase', derived from the Greek klasis, cleaving), with a prefix denoting the direction or nature of the cleavage.

From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson