Hydrothermal created emeralds Petra manufacturing enterprise offers for sale emerald and bixbite crystals, grown by a method of hydrothermal regrowth of natural beryl. Material specifications: Brand name: Petra Emerald (hydrothermal emerald) Chemical composition: Be3Al2Si6O18 Symmetry: Hexagonal Hardness (Mohs scale): 7.5-8.0 Density: 2.67-2.75 Refractive index: 1.578 - 1.572 Dispersion (C-F): 0.014 Heat resistance: up to 1250°C/2282°F