Zincite (zinc oxide)
Color: Orange, red and yellow, leek-green, light blue to colorless. Moh’s Hardness: 4-4.5
Refractive Index: 2.02
Critical Angle: 29.67°
Specific Gravity: 5.6
Fracture: Subconchoidal, brittle
Heat Sensitivity: Low
Birefringence (double refraction): Medium (.016)
Crystal Structure: Hexagonal
What I prefer to polishing with: Tin lap with Alumina oxide. Zinc laps with 8,000 pre-polish and 50,000 polish. Specta Ultalaps work pretty well. It tends to scratch and chip during polishing and can be problematic.
Jeff’s Comments: Zincite is brittle, so be careful not to shock the stone while cutting and use fine laps for roughing in.
Design Links: 4-Way Stop – This is great for saturated rough if you have a piece that will work in the shape.