Chrome chalcedony explained

Chrome chalcedony
Category:Oxide mineral
Formula:Silica (SiO2)
Molweight:60 g/mol
Color:Emerald green
System:Trigonal or monoclinic[1]
Cleavage:Absent[2]
Mohs:6–7
Fracture:Uneven, splintery, conchoidal
Luster:Vitreous, dull, greasy, silky
Streak:White
Gravity:Usually 2.60, sometimes greater than 2.62[3]
Diaphaneity:Translucent

Chrome chalcedony is a green variety of the mineral chalcedony, colored by small quantities of chromium.[4] Its name is derived from Mutorashanga, a small ferrochrome mining town in Zimbabwe where the mineral was discovered in the 1950s.[5]

It is most commonly found in Zimbabwe, where it is known as Mtorolite,[6] Mtorodite,[7] or Matorolite.[8] It is also marketed using the trade name, Aquaprase.

Chemical composition

Chrome chalcedony is similar in appearance to the better known chrysoprase, but differs in that whilst chrome chalcedony is colored by chromium (as chromium(III) oxide), chrysoprase is colored by nickel. The two can be distinguished with a Chelsea color filter, as chrome chalcedony will appear red, whilst chrysoprase will appear green.[9] Chrome chalcedony (unlike chrysoprase) may also contain tiny black specks of chromite.

Chrome chalcedony is (together with agate, carnelian, chrysoprase, heliotrope, onyx and others) a variety of chalcedony. This is a cryptocrystalline form of silica, consisting of fine intergrowths of the minerals quartz and moganite.

Locality

Chrome chalcedony (known as mtorolite, mtorodite or matorolite) occurs in Zimbabwe, principally near to the mining town of Mtoroshanga, located on the Great Dyke geological feature. It has also been discovered in western Australia, the Balkans, Bolivia, Turkey and the Ural Mountains.[10]

Ancient history

Chrome chalcedony was widely used in jewellery and seals throughout the Roman Empire. The source of the mineral is unclear, as whilst Pliny the Elder described it as coming from India, no deposits have been found there. It may have come from Anatolia (in modern-day Turkey), where deposits are known to exist.

Chrome chalcedony disappeared from use sometime in the 2nd century. It was only rediscovered when the Zimbabwean deposits were found in the 1950s.[11]

Notes and References

  1. Heaney . Peter J. . 1994 . Structure and Chemistry of the low-pressure silica polymorphs . Reviews in Mineralogy and Geochemistry . 29 . 1–40.
  2. Book: Minerals of the World. Duda, Rudolf . Rejl, Lubos. Arch Cape Press. 1990. 0-517-68030-0 . (Reference gives data for chalcedony in general.).
  3. Insider Gemologist: What Are the Identifying Characteristics of the Different Varieties of Green Chalcedony? . 7 . 13 . 2005 . GIA Insider . Gemological Institute of America.
  4. A new chrome chalcedony occurrence from Western Australia . . 23 . 265–279 . 2003 . Willing, M. J. . Stocklmayer, S.M.. Susan Stocklmayer.
  5. Web site: Murah . Mukundu . June 12, 2023 . Mtorolite Healing Properties, Mineralogy And Uses . December 31, 2023 . The Mineralogie Company.
  6. Book: Cairncross, Bruce . Field Guide to Rocks & Minerals of Southern Africa . Struik . 2005 . 1-86872-985-0.
  7. Twenty-eighth list of new mineral names . Mineralogical Magazine . 39 . 903–932 . 1974 . Hey, M. H. . Embrey, P. G. . 10.1180/minmag.1974.039.308.15 . 308 . 1974MinM...39..903H . 2009-01-22 . https://web.archive.org/web/20150610050933/http://www.minersoc.org/pages/Archive-MM/Volume_39/39-308-903.pdf . 2015-06-10 . dead .
  8. Twenty-sixth list of new mineral names . Mineralogical Magazine . 37 . 954–967 . 1970 . Hey, M. H. . 10.1180/minmag.1970.037.292.19 . 292 . 1970MinM...37..954H . 2009-01-22 . https://web.archive.org/web/20150610050521/http://www.minersoc.org/pages/Archive-MM/Volume_37/37-292-954.pdf . 2015-06-10 . dead .
  9. Book: O'Donoghue, Michael . Gems . . 0-7506-5856-8 . 2006.
  10. Chromium Chalcedony from Turkey and Its Possible Archeological Connections . Gems & Gemology: Proceedings of the 4th International Gemological Symposium & GIA Gemological Research Conference, San Diego, California . 42 . 115 . 2006 . Lule-Whipp . Cigdem . 2009-01-22 . https://web.archive.org/web/20080920163248/http://lgdl.gia.edu/pdfs/grc_2006.pdf . 2008-09-20 . dead .
  11. Web site: Ancient Glyptic Art  - Gem Engraving and Gem Carving . Lisbet . Thoresen . 2009-01-13 . https://web.archive.org/web/20081226040154/http://ancient-gems.lthoresen.com/ . 2008-12-26 . dead .

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Chrome chalcedony".

Except where otherwise indicated, Everything.Explained.Today is © Copyright 2009-2024, A B Cryer, All Rights Reserved. Cookie policy.