Beryl (Emerald & Aquamarine)
Be₃Al₂Si₆O₁₈ · Hexagonal · also called emerald, aquamarine, morganite, heliodor
Beryl grows in pegmatites, sometimes in crystals metres long. Ordinary beryl is a pale, cloudy, hexagonal prism that most people walk past; the gem varieties are the same mineral with trace chromium, iron, or manganese doing the colour work.
Properties
- Mohs hardness
- 7.5–8
- Streak
- white, colorless
- Lustre
- vitreous
- Colour
- Green beryl is emerald, blue-green is aquamarine, pink is morganite. Most beryl found in the field is opaque, milky, and pale.
- Cleavage
- Imperfect basal cleavage, rarely a factor.
- Fracture
- Conchoidal to uneven
- Specific gravity
- 2.6–2.9 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm beryl
- Six-sided prisms with flat ends and often with fine lengthwise striations.
- Scratches quartz, though only just — the difference is subtle in the field.
- Surprisingly light for a gem mineral, close to quartz in heft.
What beryl gets confused with
Each of these is settled by one test. Run that test first.
Where it is found
Granite pegmatites and some metamorphic rocks. Classic sources in Brazil, Colombia, Pakistan, and New England.
Is it worth anything?
Fine emerald rivals diamond in price per carat. Common opaque beryl is worth almost nothing, so judge by clarity and colour rather than species.