It has a defining Mohs hardness of 3, a sp of 2.71, and its luster is vitreous in crystallized varieties. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities.

Calcite is transparent to opaque and may occasionally show  fluorescence. A transparent variety called Ice land spar  is used for optical purposes. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar".

This is a Ethiopian doublet that has  been well polished. This is a doublet made from natural welo crystal mounted on to ironstone backing.We have cut the crystal a bit thicker than we would on a australian doublet. This opal is hydrophane [absorbes water] so in wet weather it will look brighter.