Beryl

Question 1

Cyclosilicates

Answer 1

Crystals consist of closed, ringlike circles of tetrahedra that share corners

Question 2

Beryl composition

Answer 2

Be3Al2Si6O18
- aluminous beryllium cycosilicate

Question 3

Beryl crystal system and habit

Answer 3

Hexagonal prisms with flat “basal” terminations
Squat tabular prisms

Question 4

Beryl physical properties

Answer 4

Hardness: 7.5-8
Colourless when pure
Basal cleavage
Fractures: conchoidal to splintery
Specific gravity: ~2.6 - ~2.9
Refractive index: 1.57 - 1.61
Fluorescence: most commonly with chromium

Question 5

Main gemstones of beryl

Answer 5

Emerald
Aquamarine
Morganite (pink)
Heliodor (yellow)
Goshenite (colourless)

Question 6

Difference between emerald and aquamarine

Answer 6

Aquamarine is found in cavities in pegmatites or alluvial deposits, and forms larger and clearer crystals
- aqua to deep blue

Emerald is found in thin veins of white calcite or quartz, dark shale, black bituminous limestone, mica or chlorite schist, or pegmatites

Question 7

What elements generate colour in beryl?

Answer 7

substitution for aluminum (+3)
emerald - chromium/vanadium
aquamarine - iron (and sodium in channels)
pink (morganite) - manganese
yellow/gold (heliodor) - iron
red (red beryl) - manganese (and no H2O in channels)
dark blue (maxixe) - NO3 in channels

Question 8

How can beryl be distinguished from other minerals?

Answer 8

• can be confused with quartz (prismatic, hexagonal)
  –> harder than quartz (7.5-8; quartz H=7)
  –> flat crystal terminations rather than pointed like quartz

Question 9

How is beryl valued?

Answer 9

non-emerald gem beryl: Type I gem
- up to ~$1,500CDN per carat (1 g=5 carats)
- red beryl is much more rare, therefore more expensive

emerald: Type III gem
- rarely clean from inclusions –> valuation is related to intensity and saturation of colour
- Colombian origin = higher premium

prices fluctuate depending on cut, clarity, hue, colour, brilliance, polish, origin, treatment

Question 10

Most common treatments for beryl

Answer 10

emerald:
- oiling - oils with similar refractive index (eg cedarwood, palm) are forced into cracks
- polymers with matching r.i. improve clarity and add durability

rough, mediocre colour:
- heat treated to bring out blue (resulting in abundance of aquamarine in market)
–> oxidized iron (Fe+3) reduced to Fe+2 when heated (gains an electron), imparting blue colouration

Question 11

Is beryl produced synthetically?

Answer 11

Yes –> synthetic emerald
- hydrothermal solution with desired chemical components dissolved into them is cooled; beryl crystals nucleate and, with time, clean stones grow