TOPICS

1. What is Beryl?
2. What varieties exist
3. Flaws / cuts
4. Geographic sources
5. Synthetics
6. Treatments

(1) What is Beryl?

• contains the element beryllium
• It is a ring silicate - the silicate tetrahedra are linked to form rings!
• it commonly grows as elongate crystals with a hexagonal cross section

COMPOSITION	Be3Al2Si6O18
HARDNESS	7.5-8.0
CRYSTAL SYSTEM	Hexagonal
COLOR	Various
PLEOCHROISM	Prominent
IMPURITIES	Various
FRACTURE	Conchoidal
SPECIFIC GRAVITY	2.36-2.91

See a movie on a beryl structure!

(2) Varieties:

(a) Emerald:

• color: GREEN
• another example of an emerald, and another another! and another emerald sample.

• emeralds can differ greatly in price and size as a consequence of thier depth and color
• due to presence of Chromium (Cr); pale green due to iron (Fe) impurities that absorb red (transmit green) and fluoresce red
• Comments

(b) Aquamarine

• Aquamarine is usually flawless. Next to emerald, it is the most highly prized of the beryls.
• color: PALE to MEDIUM BLUE (Latin for sea water); Another exampleof aquamarine. Color is due to presence of iron (Fe) in two oxidation states (ferric and ferrous) and the charge transfer between these ions
• heat treatment involves conversion of ferric to ferrous iron

(c) Heliodor (Golden Beryl) ('present of the sun')

• color due to presence of Fe-O charge transfer (and rarely, due to uranium)
• rarity and value: rarer than aquamarine, but less valued
• largest gem: 2054 ct (Smithsonian)

(d) Morganite (named after a mineral collector)

• morganite is typically a soft pink / violet, rare peach and salmon
• color due to the presence of manganese (Mn)

(e) Red Beryl

• color: red
• due to the presence of manganese (Mn)

(f) Goshenite (named after Goshen, Massachusetts)

• color: colorless
• use: used in eyeglasses

(g) Maxixe

• color: deep blue, fades
• involves irradiation effects and nitrate and carbonate groups in channels in the structure.

(3) Flaws

(a) Emerald

• crystals of emerald are very brittle
• most emeralds contain flaws:
  • inclusions (multiphase inclusions); may reveal geographic location
    • another example
  • cracks
• many emeralds are oiled, see below
• cutting emerald: THE EMERALD CUT
  • was developed specifically because emeralds are very prone to cracking when knocked.
    • cut with table perpendicular to the length of xtl -> yellowish green
    • cut with table parallel to the length of the xtl -> bluish green

(b) other beryl gems

• generally far more perfect than emerald
• few cracks or inclusions

(4) Geologic and Geographic origin:

(a) Geologic: requires source of the element Beryllium !

• veins
• hydrothermal and pegmatites
• also found with feldspar and quartz

(b) Geographic:

• Most famous: COLOMBIAN - from veins in shales and limestones
• Ancient sources: Egypt (Cleopatra's emerald mines; 2000 B.C.); Austria
  • Other: Africa, Pakistan, Brazil, USSR

(5) Synthetics

• Emerald synthesized since 1848 (no facetable gems until 1934)
  • generally not economic to synthesize aquamarine etc.
• 3 common methods: (details not required for Geology 306 students)
  • Catham (since 1940) and Gilson flux method
  • Linde hydrothermal method
  • Lechteitner hydrothermal overgrowth method.

    Make sure you understand the meaning of "hydrothermal"!

(6) Treatments

• heat treatment (irradiation)
  • most aquamarines in jewelry are heat treated (natural blue is pale)
• oiling : introduction of green oils into fractures that intersect the surfaces of faceted emeralds. This treatment makes the flaws less obvious and enhances the general appearance of the stone

(7) Trivia

Questions on the lecture

Gallery of beryl images!

"Corundum"

"Topaz"

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