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

Star Almandite Garnet

Star almandite garnet exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure. Light that strikes the inclusions within the gem reflects off of the inclusions, creating a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. Depending on the crystal, the star may have four, six, or even twelve rays. When only one band forms, it is classified as a "cat's eye".

Colors

Brownish Orange To Brownish Red, Reddish Orange To Red, Slightly Purplish Red To Reddish Purple

  • Star-almandite-garnet classification

    CommonName
    Star Almandite Garnet
    Species
    Almandite Garnet
    Variety
    Star Almandite Garnet
    Colors
    Brownish Orange To Brownish Red, Reddish Orange To Red, Slightly Purplish Red To Reddish Purple
    AlternateNames
    Star Garnet
    GemstoneGroups
    Garnet
    KeySeparations
    Appearance, refractive index, SR nature, spectrum, SG. 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
  • Star-almandite-garnet chemistry & crystallography

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

    Transparency
    Semitransparent - Semitranslucent
    Dispersion
    Strength: weak 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
  • Star-almandite-garnet characteristic physical properties

    Hardness
    7-7.5
    CharacteristicComments
    Streak
    SpecificGravity
    3.93-4.3 Typical:4.05
    Toughness
    Good
    Inclusions
    Almandite garnet is a type II clarity stone. Displays 4 or 6 rayed stars and sometimes well cut stones will show both. 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
    SubAdamantine
    Stability
    Good
    Fracture
    Conchoidal
    Cleavage
    None