Beryl Aqua marine Heliodor


Emerald Goshenite

The varieties of beryl

Beryl: golden or variety : variety Aquamarine: blue variety Morganite: variety Heliodor: greenish-yellow variety Goshenite: colourless variety

Interesting history: - were mined in ancient 4000 years ago - In the 1600’s, high quality emerald reached . - The Spaniards seized the emeralds from the Pre-Colombian people. - Mining in is still going on today, and often associated with criminal activities.

The physical properties of beryl

Group: beryl is a cyclosilicate

Luster: vitreous, transparent to translucent

Cleavage: imperfect in one direction, conchoidal

Hardness: 7.5 - 8

Specific gravity: 2.6 – 2.9 on average

Crystal habit: hexagonal prism with pincoid termination

1 The chemical properties of beryl

Beryl is a aluminum Be3Al2(Si 6O18)

Composition: BeO: 14.0%

Al2O3: 19.0% SiO2: 67.0%

The vertical hexagonal channels, which are normally vacant, can be occupied by alkali elements such as Li, Na, and Rb or neutral

molecules such as H 2O or CO2.

This image shows the hexagonal structure along the c-axis of beryl

Silica tetrahedra (upper layer)

Silica tetrahedra (lower layer)

Beryllium tetrahedra

Aluminum polyhedron

Similar but rare species include [BeAl(SiO4)(OH)] and 2+ gadolinite [YFe Be2(SiO4) 2O 2]

The crystallographic properties of beryl

Crystal system: hexagonal Point Group: 6/m 2/m 2/m Unit cell parameters: a = 9.23 Å c = 9.19Å Z = 2 : P6/mcc

c a b Beryl

Aluminum polyhedron

Silicon tetrahedron

Oxygen atom

The crystallographic properties of beryl

b a

c Beryl tetrahedron

Aluminum polyhedron

Silicon tetrahedron

Oxygen atom

2 Crystallographic data of beryl

Source: Morosin (1972)

The optical properties of beryl

Beryl is uniaxial negative (oblate indicatrix)

ww = 1.560 – 1.602 ee = 1.557 – 1.599 dd = 0.045 (3rd order interference colors)

Weak to distinct be zoned May be twinned

The thermodynamic properties of beryl

a axis Open circles are for beryl

Closed circles are for emerald

c axis

Both exhibit a negative thermal expansion along the c axis Source: Morosin (1972)

3 Occurrences of Beryl

Igneous rocks In , granite , rarely in syenite

Metamorphic rocks In low to high temperature hydrothermal veins

Associated include , , euclase, , , lepidote, , , and

Locations on : Colombia, , , , , , , (Ca, Co, Id, Ut, NC)