Charoite
| Charoite | |
|---|---|
 | |
| General | |
| Category | Silicate mineral |
| Formula (repeating unit) | K(Ca,Na) 2Si 4O 10(OH,F)•H 2O |
| IMA symbol | Cha[1] |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | P21/m |
| Identification | |
| Color | Violet, lilac, light brown |
| Crystal habit | Fibrous, massive |
| Cleavage | Good in three directions |
| Fracture | Conchoidal |
| Mohs scalehardness | 5 - 6 |
| Luster | Vitreous to pearly |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 2.54 - 2.58 |
| Optical properties | Biaxial (+) |
| Refractive index | nα= 1.550 nβ= 1.553 nγ= 1.559 |
| Birefringence | 0.009 |
| Ultravioletfluorescence | Weakly fluorescent |
| Common impurities | Al, Fe, Mn, Sr, Ba |
| Other characteristics |  Radioactive10.69% (K) |
| References | [2][3][4][5] |
Charoite(/tʃæroʊ.aɪt/CHAR-ow-ait) is a raresilicate mineralwith thechemical compositionK(Ca,Na)
2Si
4O
10(OH,F)•H
2O,first described in 1978. It is named after theChara River,despite its being 70 kilometres (43 mi) away from the discovery place.[6][3]When it was discovered, it was thought to be a fake, dyed purple to give it its striking appearance.[7]
Properties
[edit]Charoite is translucent lavender to purple in color with a pearly luster. Charoite is strictly massive in nature, and fractures areconchoidal.It has an unusual swirling, fibrous appearance, sometimeschatoyant,and that, along with its intense color, can lead many to believe at first that it is synthetic or enhanced artificially. Though reportedly discovered in the 1940s, it was not known to most of the world until its description in 1978. It is said to be opaque and unattractive when found in the field; a fact that may have contributed to its late recognition.[5]Charoite consists of oxygen (43.75%), silicon (27.65%) and calcium (17.53%) mainly, but its composition includes potassium (10.69%) - which gives it its radioactive properties - and hydrogen (0.39%) as well. It has a barely detectable, 0.65% radioactivity concentration perGamma Ray American Petroleum Institute Units.[3]
Inclusions mainly come in the swirly patterns of the mineral.[8]The black spots on some specimens are eitheraugiteoraegirine,the latter occurring in almost all charoites since they commonly grow together. Larger round greenish spots arefeldspar.Lighter colored stones or ones with translucent areas are likely due tocanasite.The yellowish brown spots aretinaksite,which was discovered at the same time as charoite was. Charoite's silky, fibrous structure results in a shimmery looking polished stone. Sometimes, the very white flashes are tiny white feldspar.[7]Sugilitesand charoites can be confused, as both are purple, and sugilite can have black and white inclusions, however sugilite lacks the swirling pattern that are present in charoite stones, and it also lacks the chatoyant effect.[8]
Occurrences
[edit]It has been reported only from theAldan Shield,Sakha Republic,Siberia, Russia. It is found where asyeniteof theMurun Massifhas intruded into and alteredlimestonedeposits producing apotassium feldsparmetasomatite,[5]and forms between 200 - 250 °C.[3]Tinaksite, canasite and charoite are associated and black aegirine is also common where these three minerals grow. Common impurities includealuminium,iron,manganese,strontiumandbarium.[7]Charoitite is a rock like lapis lazuli, but unlike the latter one, charoitite mostly consists of the mineral charoite.[9]
Marketing and uses
[edit]When it arrived to the western market, it was already named charoite. Common tradenames include charoite jade and lilac stone. Although considering its rarity and only type locality, even the highest quality charoite gemstones cost only a few dollars a carat, usually costing between 1.10 - $3 per carat.[9][10]In its price, color and chatoyancy are the main factors. Chatoyant translucent varieties are the most sought after, as while chatoyancy already being uncommon in the mineral, translucent varieties are rarer than the more common opaque ones.[8]Alongside jewelry, due to the fact that the material can be massive in size, charoite can be used in the making of bookends, vases, goblets, boxes, or in small statues. Despite its relatively high hardness, it makes poor center pieces in rings and in bracelets. As it is a heat sensitive mineral, the mechanical cleaning of it should be avoided. It is recommended to use mild detergents and soft brushes or a cloth to clean it, and to never use strong and toxic detergents on it.[8][9]
Gallery
[edit]-
Charoitite, a charoite-dominated potassic metasomatite rock from the type area. Photo is 5.7 cm wide. -
Charoite postage stamp, 2000, from a series commemorating "300 Years of Mining and Geological Service in Russia."
References
[edit]- ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3): 291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
- ^Mineralienatlas
- ^abcdBarthelmy, David (2014)."Charoite Mineral Data".Webmineral.Retrieved2022-04-12.
- ^Charoite,Mindat.org,retrieved4 July2022
- ^abcAnthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005)."Charoite"(PDF).Handbook of Mineralogy.Mineral Data Publishing. Archived fromthe original(PDF)on 7 November 2022.Retrieved4 July2022.
- ^Ian Frazier,Travels in Siberia,Farrar, Straus and Giroux, New York (NY), 2010, ISBN 978-0-374-27872-4,page 394
- ^abc"Charoite Meaning, History and Detailed Information with Photos".Cape Cod Crystals.Retrieved2022-04-12.
- ^abcd"What is Charoite? – A Complete Buying Guide | Jewelry Guide".Retrieved2022-04-12.
- ^abc"Charoite Value, Price, and Jewelry Information".International Gem Society.Retrieved2022-04-12.
- ^"Charoite Information - Gorgeous purple gemstone from Siberia".gemselect.Retrieved2022-04-12.
Gemmological classifications by E. Ya. Kievlenko (1980), updated | |||||||||
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