Chrome chalcedony

Zimbabwean chrome chalcedony (known locally as mtorolite). Scale is in centimetres.

General
Category| Tectosilicate minerals, quartz group, chalcedony variety
Formula
(repeating unit)| Silica (SiO2)
Crystal system| Trigonal (quartz), monoclinic (moganite)[1]
Identification
Formula mass| 60 g/mol
Color| Emerald green
Cleavage| Absent[2]
Fracture| Uneven, splintery, conchoidal[2]
Mohs scale hardness| 6–7[2]
|re|er}}| Vitreous, dull, greasy, silky[2]
Streak| White
Diaphaneity| Translucent[2]
Specific gravity| Usually 2.60, sometimes greater than 2.62[3]

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.

## Contents

* 1 Chemical composition
* 2 Locality
* 3 Ancient history
* 4 References

## 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.[4] The two can be distinguished with a Chelsea color filter, as chrome chalcedony will appear red, whilst chrysoprase will appear green.[4][9] Chrome chalcedony (unlike chrysoprase) may also contain tiny black specks of chromite.[3]

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.[1]

## 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.[6] 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.[10]

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

## References

1. ↑ 1.0 1.1 Heaney, Peter J. (1994). "Structure and Chemistry of the low-pressure silica polymorphs". Reviews in Mineralogy and Geochemistry 29: 1–40.
2. ↑ 2.0 2.1 2.2 2.3 2.4 Duda, Rudolf; Rejl, Lubos (1990). Minerals of the World. Arch Cape Press. ISBN 0-517-68030-0(Reference gives data for chalcedony in general.)
3. ↑ 3.0 3.1 "Insider Gemologist: What Are the Identifying Characteristics of the Different Varieties of Green Chalcedony?". GIA Insider (Gemological Institute of America) 7 (13). 2005. http://www.gia.edu/newsroom/issue/2798/2372/insider_newsletter_details.cfm#3.
4. ↑ 4.0 4.1 4.2 Willing, M. J.; Stocklmayer, S.M. (2003). "A new chrome chalcedony occurrence from Western Australia". Gems & Gemology 23: 265–279.
5. ↑ Murah, Mukundu (June 12, 2023). "Mtorolite Healing Properties, Mineralogy And Uses". https://themineralogiecompany.com/the-mineralogist/mtorolite-healing-properties-benefits-and-uses/.
6. ↑ 6.0 6.1 Cairncross, Bruce (2005). Field Guide to Rocks & Minerals of Southern Africa. Struik. ISBN 1-86872-985-0.
7. ↑ Hey, M. H.; Embrey, P. G. (1974). "Twenty-eighth list of new mineral names". Mineralogical Magazine 39 (308): 903–932. doi:10.1180/minmag.1974.039.308.15. Bibcode: 1974MinM...39..903H. http://www.minersoc.org/pages/Archive-MM/Volume_39/39-308-903.pdf. Retrieved 2009-01-22.
8. ↑ Hey, M. H. (1970). "Twenty-sixth list of new mineral names". Mineralogical Magazine 37 (292): 954–967. doi:10.1180/minmag.1970.037.292.19. Bibcode: 1970MinM...37..954H. http://www.minersoc.org/pages/Archive-MM/Volume_37/37-292-954.pdf. Retrieved 2009-01-22.
9. ↑ O'Donoghue, Michael (2006). Gems. Butterworth-Heinemann. ISBN 0-7506-5856-8.
10. ↑ 10.0 10.1 Lule-Whipp, Cigdem (2006). "Chromium Chalcedony from Turkey and Its Possible Archeological Connections". 42. pp. 115. http://lgdl.gia.edu/pdfs/grc_2006.pdf. Retrieved 2009-01-22.
11. ↑ Thoresen, Lisbet. "Ancient Glyptic Art - Gem Engraving and Gem Carving". http://ancient-gems.lthoresen.com/.

* v
* t
* e

Silica minerals

Crystalline|

* Coesite
* Cristobalite
* Keatite
* Moganite
* Quartz
* Seifertite
* Stishovite
* Tridymite

Cryptocrystalline|

* Chalcedony
* Chert
* Flint
* Jasper

Amorphous|

* Fulgurite
* Lechatelierite
* Opal

Miscellaneous|

* Tiger's eye

Notable varieties|

| Chalcedony|

* Agate
* Carnelian
* Chrysoprase
* Heliotrope
* Onyx

|

Opal|

* Fiorite
* Geyserite

Quartz|

* Amethyst
* Ametrine
* Herkimer diamond
* Smoky quartz
* Shocked quartz
* Prasiolite

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