How the Earth was Formed
Mining of Metals
Agate gem stone
Amber gem stone
Beryl gem stone
Chrysolite gem stone
Crystalline Quartz gem stones
Diamond gem stone and Corundum
Epidote gem stone
Feldspar gem stone<
Garnet gem stone
Lapis Lazuli gem stone
Malachite gem stone
Obscurely Crystalline Quartz gem stones
Opal gem stone
Ornamental gem stones
Topaz gem stone
Tourmaline gem stone
Turquoise gem stone
Quartz and the Silicates
Mineral Guide > Precious Stones > Feldspar gem stone
Feldspar gem stoneFeldspar is the family name of several minerals closely related, and, indeed, grading into each other, but distinguished by mineralogists by separate specific terms. These minerals are all silicates of aluminum, with some alkali or alkali earth, having a hardness of about 6 in the scale in which quartz is 7.
As ornamental stones only certain varieties of feldspar are valued and their value depends on accidents of color or structure. The first of the feldspars which may be mentioned as being prized as an ornamental stone is amazonstone or green feldspar.
It is only to the green variety that the name of amazonstone is applied, a name meaning stone from the Amazon River.
The second species of feldspar which may be mentioned as of use as an ornamental stone is labradorite. This differs in composition from amazonstone in containing soda and lime in place of potash.
The gems known as moonstone and sunstone owe the play of colors which gives them their respective names to similar causes. These gems are generally some form of feldspar, although any mineral giving a similar sheen of color might be included under them.
The Ceylon moonstone is sometimes known as Ceylon opal, but it is the variety of feldspar known as orthoclase, which is a potash feldspar.
Sunstone is the term by which those kinds of feldspar are known which reflect a spangled yellow light.
Both sunstones and moonstones can be accurately imitated in glass and the distinction of the artificial from the real by ocular examination alone would be almost impossible.
Gems are occasionally cut from other forms of feldspar than those here described, which are transparent and colorless and valued for their luster.