Provenite

About Rock crystal

SiO₂

Rock crystal is the colourless variety of quartz. Its lack of colour reflects the absence of colour-causing impurities and colour centres. It is the clear counterpart of smoky quartz, amethyst and citrine. Synthetic hydrothermal quartz is also made as colourless crystal, so provenance matters.

Show 7 localities on the map

Photos of Rock crystal

Group of colorless, transparent quartz crystals in graduated ascending rows (specimen from Madagascar).
Rock crystal · Madagascar
Group of colorless, transparent quartz crystals in graduated ascending rows (specimen from Madagascar).
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source
Dense cluster of water-clear quartz points rising from a thin matrix plate (specimen from East Coleman Mine, Jessieville, Garland County, Arkansas, USA).
Rock crystal · East Coleman Mine
Dense cluster of water-clear quartz points rising from a thin matrix plate (specimen from East Coleman Mine, Jessieville, Garland County, Arkansas, USA).
Photo: Robert M. Lavinsky · CC BY-SA 3.0 · Source

Where Rock crystal is found (7)

Greenland

Hungary

Madagascar

Switzerland

United States

Identity

Variety of
Quartz
Also called
Colourless quartz
Strunz
4.DA.05 · 4 Oxides and hydroxides
IMA status
Variety
Name origin
From Greek kristallos (crystal); the ancient Greeks, including Theophrastus, used the name for clear quartz, which was believed to be permanently frozen ice.
Elements
Si, O

Physical properties

Color
Colourless
Luster
Vitreous luster
Transparency
Transparent
Mohs hardness
7
Density
2.65–2.66 g/cm³
Cleavage / fracture
Cleavage rarely observable and poor on {10-11}, {01-11} and {10-10}; rhombohedral parting; fracture conchoidal

Crystallography

Crystal system
Trigonal
Space group
P3₁21 or P3₂21
Typical habit
Prismatic crystals with rhombohedral terminations; also doubly terminated crystals (for example Herkimer type) and large cleft crystals and clusters
Twinning
Very common: Dauphiné and Brazil penetration twins, Japan contact twins
Optical data
Uniaxial (+); omega = 1.544, epsilon = 1.553

Formation and use

Formation
Found in Alpine fissures (clefts) in granitic massifs, in sandstone-hosted hydrothermal veins, in vugs in carbonate rock (dolostone), and in sulfide-bearing hydrothermal veins. Alpine cleft crystals grow slowly over millions of years from metamorphic fluids as the Alps rise and cool toward about 200 degrees C.
Uses
Used since prehistoric times for cutting tools and from the Middle Ages for carved objects such as monstrances and reliquaries (workshops in Milan, Venice, Prague, Freiburg); quartz in general serves in frequency standards and optical instruments; collector's specimens.
Stability and care
Natural rock crystal needs no treatment to be colourless, so the main concern is synthetic material, which is grown in large, high-quality pieces. A reliable separation uses infrared spectroscopy: natural rock crystal shows absorptions near 3379, 3483 and 3595 cm-1 that synthetic quartz never shows. Nail-head spicules and breadcrumb-like inclusions are typical of hydrothermal synthetics, while Brazil-law twinning points to natural origin.

Related minerals

Related minerals
Quartzsmoky quartzamethystcitrineprasioliterose quartz
Can be confused with
Synthetic (hydrothermal) colourless quartz

Sources

  1. SRC-084 · Book
    Handbook of Mineralogy - QuartzAnthony, J.W.; Bideaux, R.A.; Bladh, K.W.; Nichols, M.C. · 2001 · Mineralogical Society of America / Mineral Data Publishing
  2. SRC-085 · Database
    Quartz (Mindat.org mineral page)Mindat.org / Hudson Institute of Mineralogy
  3. SRC-134 · Article
    Quartz crystals from alpine fissures: their formation and the historical significance of alpine quartz as raw material for objets d'artHuegi, M.F. · 2023 · 37th International Geological Congress (IGC), Tokyo
  4. SRC-139 · Website
    Herkimer diamondsKing, H.M. · Geology.com
  5. SRC-144 · Article
    Synthetic Rock Crystal Quartz Bangle with Unusual InclusionsNg-Pooresatien, N. · 2015 · Gems & Gemology, Winter 2015, Lab Notes

Draft data from the Provenite workbook. Check entries against the cited sources before relying on them. Photos are open-licence images from Wikimedia Commons; the author and licence are given with each photo.