Almandite Garnet | Gemopedia

Though they all have the same crystal structure (cubic, like diamond and spinel), garnet is an entire group of minerals that vary in their chemical composition, resulting in a variety of gems featuring different colors and properties. Though some varieties of red garnet are common and found on nearly every continent on Earth, other garnets like orange spessartite, green demantoid and tsavorite, are much less abundant. There are more than 20 garnet species, but the five most important include pyrope and almandite (the combination of which creates rhodolite), spessartite, grossularite or grossularite (which includes hessonite and tsavorite), and andradite (which includes demantoid). Garnets of all species are the birthstone for January, so January babies aren't limited to the well-known red varieties.
Alternate Names
Almandine Garnet
Colors
Brownish Orange To Brownish Red To Purplish Red

Almandite Garnet Classification

Common Name

Almandite Garnet

Species

Almandite Garnet

Variety

Colors

Brownish Orange To Brownish Red To Purplish Red

Alternate Names

Almandine Garnet

Gemstone Groups

Garnet

Key Separations

refractive index, SR nature and spectrum. Color is also helpful. Stones with SG lower than 3.8 and a RI lower than 1.76 are pyrope and those with higher almandine.

Comments

Misnomers: Colorado ruby or Cape ruby.Some large stones are cut shallow because the dark saturation and concave back cabochons can also be found.

Almandite Garnet Optical Properties

Transparency

Transparent - Semitranslucent

Refractive Index

Over The Limit 1.78-1.82
Tolerance:(+0.030/-0.030)

Birefringence

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

Singly Refractive (SR) With ADR

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

None

Dispersion

Strength: moderate fire Value: 0.024

Comments

Almandite Garnet Chemistry & Crystallography

Chemical Name

iron aluminum silicate

Chemical Formula

Fe3Al2(SO4)3

Synthesis

Crystal System

Cubic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Almandite Garnet Characteristic Physical Properties

Hardness

7-7.5

Streak

Specific Gravity

3.93-4.3 Range:0.25/-0.12 Typical:4.05

Toughness

Good

Inclusions

Almandite garnet is a type II clarity stone. Stones are often found with needles that intersect at 70o to 110o angles. Zircon crystals are commonly seen with strain halos. Irregular or rounded crystals can also be found.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal

Cleavage

None

Comments

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