Coloured stones
Corundum, beryl, and tourmaline viewed through chemistry, optical behaviour, treatment history, and responsible language.
Ruby
Chromium-bearing red corundum, valued through colour, transparency, origin evidence, and treatment status.
Ruby belongs to the corundum family. Chromium produces red, while iron modifies appearance and fluorescence. Heat treatment is widely encountered; filling and diffusion require different disclosure because they alter value and care considerations in materially different ways.
- Crystal system
- Trigonal
- Mohs hardness
- 9
- Refractive index
- Approximately 1.762-1.770
Emerald
Green beryl whose fractures, clarity enhancement, and geological context demand careful disclosure.
Emerald is coloured by chromium, vanadium, or both. Fissures are common and may be filled with oils or resins to reduce their visibility. Reports should distinguish the identity of the stone from the degree of clarity enhancement and any supported origin opinion.
- Crystal system
- Hexagonal
- Mohs hardness
- 7.5-8
- Typical treatment
- Fissure filling
Tourmaline
A chemically complex group capable of vivid colour zoning and strong pleochroism.
Tourmaline is a mineral group rather than a single uniform species. Elbaite supplies many gem colours, while copper-bearing material can display intense blue to green. Long prismatic growth, colour zoning, and directional colour strongly influence cutting choices.
- Crystal system
- Trigonal
- Mohs hardness
- 7-7.5
- Optical character
- Doubly refractive, pleochroic