Rare gems
Materials encountered less often, where small datasets and unfamiliar names make cautious identification especially important.
Alexandrite
Chromium-bearing chrysoberyl known for a light-source-dependent colour change.
Fine alexandrite shifts from greenish hues in daylight-equivalent light toward red or purplish hues under incandescent light. The strength, balance, and extent of that change matter alongside transparency, cut, and size.
- Crystal system
- Orthorhombic
- Mohs hardness
- 8.5
- Phenomenon
- Colour change
Red beryl
A manganese-coloured beryl usually seen in small, included crystals.
Red beryl is associated most famously with rhyolitic deposits in Utah. Facetable material is scarce, and clean stones of meaningful size are exceptional. Its beryl identity does not make it an emerald, despite both belonging to the same mineral species.
- Colouring element
- Manganese
- Crystal system
- Hexagonal
- Noted locality
- Wah Wah Mountains, Utah
Benitoite
A vivid blue barium titanium silicate and the state gem of California.
Benitoite combines high dispersion with a sapphire-like blue that can disguise its identity at first glance. Its principal historic source, the Benitoite Gem Mine area in San Benito County, produces crystals often associated with natrolite and neptunite.
- Crystal system
- Hexagonal
- Mohs hardness
- 6-6.5
- Notable response
- Blue fluorescence under short-wave UV