Almandite Garnet Gemstone & Information | Gemopedia by JTV | Gemopedia™

Almandite Garnet

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.

Colors

Brownish Orange To Brownish Red To Purplish Red

  • Almandite-garnet classification

    CommonName
    Almandite Garnet
    Species
    Almandite Garnet
    Variety
    Colors
    Brownish Orange To Brownish Red To Purplish Red
    AlternateNames
    Almandine Garnet
    GemstoneGroups
    Garnet
    KeySeparations
    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.
    ClassificationComments
    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 chemistry & crystallography

    ChemicalName
    iron aluminum silicate
    ChemicalFormula
    Fe3Al2(SO4)3
    Synthesis
    CrystalSystem
    Cubic
    ChemistryClassification
    Silicate
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Almandite-garnet optical properties

    Transparency
    Transparent - Semitranslucent
    Dispersion
    Strength: moderate fire Value: 0.024
    OpticalComments
    RefractiveIndex
    Over The Limit 1.78-1.82
    Tolerance:(+0.030/-0.030)
    Birefringence
    OpticCharacter
    NA
    OpticSign
    NA
    PolariscopeReaction
    Singly Refractive (SR) With ADR
    Fluorescence
    SWUV: Inert
    LWUV: Inert
    CCFReaction
    Pleochroism
    None
  • Almandite-garnet characteristic physical properties

    Hardness
    7-7.5
    CharacteristicComments
    Streak
    SpecificGravity
    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