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Geosciences LibreTexts

16.05.07: Sunset Quartz

  • Page ID
    4093
  • Sunset Quartz
    Chemical composition SiO2 Silicon dioxide
    Crystal system Trigonal
    Habit Prismatic
    Cleavage Poor
    Fracture Conchoidal
    Hardness 7
    Optic nature Uniaxial +
    Refractive index 1.544 - 1.553
    Birefringence 0.009
    Dispersion 0.013
    Specific gravity 2.65
    Lustre Vitreous
    Pleochroism None

    Sunset quartz is a variety of quartz in very limited supply. It was discovered in 2006 in Minas Gerais, Brazil, with the vein producing only 5 kg. of gem quality material total. The collection pictured above, belonging to Karim Moussally, is one of the largest personal collections in existence.
    The yellowish and orange color of the quartz is the result of microscopic acicular (needle-like) inclusions.

    File:Sunset inclusion.jpg

    Figure \(\PageIndex{1}\): Acicular Incusions in Sunset Quartz: 40X
    Photo courtesy of Barbra Voltaire


    Analysis of these inclusions, reported in Gems & Gemology in Winter 2006, determined that they were NOT rutile as we might have suspected but were composed of Si, Al and Fe with traces of K! The identification of the actual mineral was inconclusive, but it has been speculated that it could possibly be acicular limonite.
    The material is semi-transparent to translucent with a milky consistency.
    The RI, Birefringence, SG (see template on the right) is typical of quartz.