Chemical Characteristics of Moonstone

Crystal Group

• All gems are divided into seven crystal groups, determined by geometric and molecular characteristics. Moonstone is in the "monoclinic" group, which indicates its crystal structure of three asymmetrical axes. Two of these intersect and are perpendicular to the third. Moonstone is also classified as a type of orthoclase feldspar.

Chemical Composition and Refractive Index

• The chemical composition of moonstone is KAlSi3O8. This composition determines all of its other properties. When specially heat treated to modify its color, the moonstone's chemical composition is changed. The refractive index measures the difference between the speed of light in air and the speed of light in the material. Most gems have their own refractive index. Moonstone measures from 1.518 to 1.526.

Color

• Moonstone's color is commonly white or bluish white. It is translucent, which allows for dynamic optical effects in which the moonstone's surface changes as it reflects light at changing angles. This play of light is called "adularescence," and is the origin of its celestial name. The precise opacity of its color plays a crucial role in determining the value of a particular sample of moonstone.

Density and Hardness

• A material's density is measured by its weight in relationship to an equal volume of water. Water sets the standard at 1.00 g per cubic centimeter, or 1.00 g/cc. Moonstone's density measures from 2.55 to 2.57 g/cc. Hardness is measured by the Mohs scale of hardness, in which a material is measured between one and 10. Talc is the softest at one, and diamond is the hardest at 10. Moonstone's hardness measures from six to 6.5, between feldspar and quartz.