Helidore (Beryl)

Color: yellow, yellow/green

Moh’s Hardness: 7.5-8

Refractive Index: 1.57-1.60

Critical Angle: 39.97°

Specific Gravity: 2.65-2.75

Cleavage: None

Fracture: Conchoidal, tough

Dispersion: Medium (.014)

Heat Sensitivity: Slightly

Dichroism: weak (gold-yellow to greenish-yellow)

Birefringence (double refraction): Weak (.006-.009)

Crystal Structure: Hexagonal

Treatments: Often heat treated and irradiated