Asterism is caused by light reflecting from minute needle-like crystal impurities that are present in the host mineral. These tiny crystals are aligned with specific growth planes depending on the host minerals' crystal structure. The crystal structure and number of planes determine the shape and number of rays in the star.

The following gemstones are in my collection. They are not for sale. The images are thumbnails. Click on the image for an enlarged view.

Star Garnet, Almandine
     Composition: Fe₃Al₂Si₃O₁₂
     4 & 6 Rays
     Asterism caused by Rutile
     Degrees: 4 Ray =0, 70 degrees
     6 Ray = 0, 70, 110 degrees
     Crystal: Isometric

Star Quartz - Rose
     Composition: SiO₂
     6 Rays
     Asterism caused by Rutile
     Degrees: 0, 60, 120 degrees
     Crystal: Hexagonal

Star Ruby
Star Sapphire
     Composition Al₂O₃
     6 Rays
     Asterism caused by Rutile
     Degrees: 0, 60, 120 degrees
     Crystal: Hexagonal

Star Spinel
     Composition: MgAl₂O₄
     4 & 6 Rays
     Asterism caused by Rutile ?
     Degrees: 4 Ray = ? degrees
       6 Ray = 0, 60, 120 degrees
     Crystal: Isometric

Star Sillimanite
     Composition Al₂SiO₅
     4 & 6 Rays
     Asterism caused by Magnetite
     Degrees: 4 Ray 0, 7.5, 76 degrees;
     6 Ray 0, ? degrees
     Crystal: Orthorhombic

Star Sunstone
     Composition: NaAlSi₃O₈
     4 Rays
     Asterism caused by:
        Oregon Var.: Copper
        Everywhere else: Hematite
     Degrees: 90
     Crystal: Monoclinic

Star Moonstone
     Composition: KaAlSi₃O₈
     4 Rays
     Asterism caused by ?
     Degrees: 90 Degrees
     Crystal: Monoclinic

Star Diopside, Black
     Composition: CaMgSi₂O₆
     4 Rays
     Asterism caused by Magnetite
     Degrees: 0, 73 degrees
     Crystal: Monoclinic

DIC vs Polarized

Star Chrysoberyl
     Composition BeAl₂O₄
     4 Rays
     Asterism caused by ?
     Degrees: 90?
     Crystal: Orthorhombic

01/26/09