Star Sapphire Gemstone & Information | Gemopedia by JTV | Gemopedia™

Star Sapphire

Star sapphire 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 typically has six rays, but on occasion, twelve rays.

Colors

Blue, Black, Brown, Green, Purple, Plum, Rarely Orange, Yellow; If Any Other Color Than Blue Designate By Color

  • Star-sapphire classification

    CommonName
    Star Sapphire
    Species
    Corundum
    Variety
    Star Sapphire
    Colors
    Blue, Black, Brown, Green, Purple, Plum, Rarely Orange, Yellow; If Any Other Color Than Blue Designate By Color
    AlternateNames
    GemstoneGroups
    KeySeparations
    appearance, RI and magnification
    ClassificationComments
    Stone usually cut as cabochons. Black star sapphires cover black dark brown, green and dark blue.
  • Star-sapphire chemistry & crystallography

    ChemicalName
    aluminum oxide
    ChemicalFormula
    Al2O3
    Synthesis
    CrystalSystem
    Hexagonal
    ChemistryClassification
    Oxide
    Nature
    Natural
    Crystallinity
    Crystalline
    ChemistryComments
  • Star-sapphire optical properties

    Transparency
    Semitransparent - Opaque
    Dispersion
    Strength: weak fire Value: 0.018
    OpticalComments
    RefractiveIndex
    1.762-1.77
    Tolerance:(+0.009/-0.005)
    Birefringence
    0.008-0.01
    OpticCharacter
    Uniaxial
    OpticSign
    Negative
    PolariscopeReaction
    Doubly Refractive (DR)
    Fluorescence
    SWUV: Inert to strong red
    LWUV: Inert to strong red
    CCFReaction
    Pleochroism
    Unobservable
  • Star-sapphire characteristic physical properties

    Hardness
    9
    CharacteristicComments
    Streak
    White
    SpecificGravity
    4.1-3.95 Typical:4
    Toughness
    Excellent
    Inclusions
    Star sapphires will have silk or sets of parallel rutile needles that produce a 6-ray star, hexagonal growth lines, color zoning and mineral inclusions. Weak and less well formed stars along with weaker body color is typical of natural stones. In natural stones at least one ray of the start will be perpendicular to the hexagonal growth zones. Stone with 12-rayed stars are rare but typically occur in dark blue or black stones.
    Luster
    SubAdamantine
    Stability
    Very Good
    Fracture
    Conchoidal
    Cleavage
    None