Achroite Tourmaline Faceting Information
Color: (Greek – without color) colorless or nearly so, fairly rare
Moh’s Hardness: 7-7.5
Refractive Index: 1.616-1.652
Critical Angle: 38.23°
Specific Gravity: 3.02-3.26
Fracture: Uneven, small conchoidal
Heat Sensitivity: Can be, but usually no problems
Dichroic: Strong (many color variations), on colorless material obviously not generally present
Birefringence (double refraction): Medium (.014-.024)
Crystal structure: Hexagonal
Treatments: Heat treating to lighten colors is common and sometimes material will go clear (Achroite).
What I prefer to polishing with: Alumina oxide with a tin lap (scored).
Jeff’s Comments: Cuts and polishes like any other Tourmaline, usually no problems. Orientation is not needed on clear colorless rough, cut on the “c” axis if it is convenient. Sometimes you can find a piece of rough like the stone above that has a spot of color surrounded by clear. This type of stone is fairly uncommon but as you can see makes a very interesting finished gem if you can find one. Orientate the color spot in the middle of the stone, below the girdle line and toward the tip of the pavilion. Be sure and check the color spot from all directions before cutting, so that it is centered up.
Design Notes: About any deep Tourmaline designs will work well.
Design Links: Signature #4 – This is good for about any rough
Easy Emerald – This is a classic and works well on poor “c” axis colored stones
Smith Bar – This is a classic and works well on poor “c” axis colored stones