Hardness; is 6 to 6 1/2 on mohs scale.
Specific Gravity; 2.5 to 2.6
Optical; Translucent to nearly opaque with a sheen called adularescence that resembles a cloud of light with in the stone when held and viewed at the correct angle to the eye.
Cool to touch and has a waxy luster or feels slick.

Moonstone is a gem from the large group of minerals called feldspars, they are the most abundant minerals in the earth’s crust. All are aluminum silicates containing calcium, potassium or sodium.

The potassium members include microcline and orthoclase. The rest of the feldspars form the plagioclase group. They are classified according to the amount of calcium and sodium present. The six minerals in the plagioclase group are albite, anorthite, andesine, bytownite, labradorite, and oligoclase.

Blue moonstone is the most prized of the microcline gems.The feldspars have a hardness of 6 to 6 1/2 which is relatively low for a gem.

Moonstone is a microcline gem and the blue or white sheen is caused by the presence of tiny crystals of albite arranged in layers within the microcline. It may be completely transparent and the sheen can be silvery white or a soft distinct blue. The sheen resembles a cloud of light that appears within the gem when viewed at the correct angle to the eye.

Moonstones tend to be translucent to nearly opaque. Some moonstones are found in the color shades of beige, brown, gray, white, green, pink or yellow.

Most of these are cut as high domed cabochons and the sheen is concentrated at the top in a bright spot that often extends across the stone as a distinct eye, these are called cats-eye moonstone. Others may have a second ray at right angles to the first and forming a cross.