Almandine


One of six end members of the garnet family. Pure almandine garnets are virtually non-existent. There is always a mixture with pyrope and/or spessartite. To be classed as an almandine SG should be >3.93 and RI >1.77 (There is a small difference in limit values depending on source).

Physics:

Chemistry: Fe+23Al2(SiO4)3
Hardness: 7–7,5
SG: 3,93–4,32
Cleavage: None
Toughness: Sometimes slightly brittle
Heat sensitivity: None

Cutting lap: 

RI: 1,77–1,83
Dispersion: 0,024 (medium)
Birefringence None
Pleochroism: None
Critical angle: 34,5°

Cutting angles (culet/crown):

Vargas: 41°/39°
Olson: 39°/37°
Soukup: 42°/37°
Roth: 42°/37°
MDR: 42°/37°
Schlagel: 40°/36°

Cutting lap: 

Medium – fine

Facet polishing:

Vargas: Alumina oxide on tin/lead, tin oxide on tin
Olson: Chrome oxide on tin
Soukup: Alumina oxide on tin or tin/lead
Christiansen: Alumina oxide on tin/lead, tin oxide on tin

Cabochon polishing:

Olson: Chrome oxide on leather
Christiansen: Alumina, tin or chrome oxide on leather or wood
Cox: Alumina or chrome oxide on leather, Cerium oxide on felt
Covington: Chrome or cerium oxide on felt

Orientation:

For best yield

Treatments/synthetics:

None known

Hint !

Almandine can sometimes be to brittle for new cutting laps.


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