| Cassiterite | |
|---|---|
 Cassiterite surrounded bymuscovite, from Xuebaoding, Huya, Pingwu, Mianyang, Sichuan, China (size: 100 × 95 mm, 1128 g) | |
| General | |
| Category | Oxide minerals |
| Formula | SnO2 |
| IMA symbol | Cst[1] |
| Strunz classification | 4.DB.05 |
| Crystal system | Tetragonal |
| Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
| Space group | P42/mnm |
| Unit cell | a = 4.7382(4) Å, c = 3.1871(1) Å; Z = 2 |
| Identification | |
| Color | Black, brownish black, reddish brown, brown, red, yellow, gray, white; rarely colorless |
| Crystal habit | Pyramidic, prismatic, radially fibrous botryoidal crusts and concretionary masses; coarse to fine granular, massive |
| Twinning | Very common on {011}, as contact and penetration twins, geniculated; lamellar |
| Cleavage | {100} imperfect, {110} indistinct; partings on {111} or {011} |
| Fracture | Subconchoidal to uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 6–7 |
| Luster | Adamantine to adamantine metallic, splendent; may be greasy on fractures |
| Streak | White to brownish |
| Diaphaneity | Transparent when light colored, dark material nearly opaque; commonly zoned |
| Specific gravity | 6.98–7.1 |
| Optical properties | Uniaxial (+) |
| Refractive index | nω = 1.990–2.010 nε = 2.093–2.100 |
| Birefringence | δ = 0.103 |
| Pleochroism | Pleochroic haloes have been observed. Dichroic in yellow, green, red, brown, usually weak, or absent, but strong at times |
| Fusibility | infusible |
| Solubility | insoluble |
| References | [2][3][4][5][6] |
Cassiterite is atinoxide mineral,SnO2. It is generallyopaque, but it is translucent in thin crystals. Itsluster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tinore throughoutancient history and remains the most important source of tin today.
Most sources of cassiterite today are found inalluvial orplacer deposits containing the weathering-resistant grains. The best sources of primary cassiterite are found in the tin mines ofBolivia, where it is found in crystallisedhydrothermal veins.Rwanda has a nascent cassiterite mining industry. Fighting over cassiterite deposits (particularly inWalikale) is a major cause of the conflict waged in eastern parts of theDemocratic Republic of the Congo.[7][8] This has led to cassiterite being considered aconflict mineral.
Cassiterite is a widespread minor constituent ofigneous rocks. The Bolivian veins and the 4500 year old workings ofCornwall andDevon,England, are concentrated in high temperaturequartz veins andpegmatites associated withgraniticintrusives. The veins commonly containtourmaline,topaz,fluorite,apatite,wolframite,molybdenite, andarsenopyrite. The mineral occurs extensively inCornwall as surface deposits onBodmin Moor, for example, where there are extensive traces of a hydraulic mining method known asstreaming. The current major tin production comes from placer or alluvial deposits inMalaysia,Thailand,Indonesia, theMaakhir region ofSomalia, andRussia.Hydraulic mining methods are used to concentrate mined ore, a process which relies on the highspecific gravity of the SnO2 ore, of about 7.0.
Crystal twinning is common in cassiterite and most aggregate specimens show crystal twins. The typical twin is bent at a near-60-degree angle, forming an "elbow twin".Botryoidal or reniform cassiterite is calledwood tin.
Cassiterite is also used as agemstone and collector specimens when quality crystals are found.
The name derives from theGreek κασσίτερος (transliterated as "kassiteros") for "tin".[9] Early references to κασσίτερος can be found inHomer'sIliad, such as in the description theShield of Achillies. For example, the passage in book 18 chapter 610:
αὐτὰρ ἐπεὶ δὴ τεῦξε σάκος μέγα τε στιβαρόν τε,
610τεῦξ᾽ ἄρα οἱ θώρηκα φαεινότερον πυρὸς αὐγῆς,
τεῦξε δέ οἱ κόρυθα βριαρὴν κροτάφοις ἀραρυῖαν
καλὴν δαιδαλέην, ἐπὶ δὲ χρύσεον λόφον ἧκε,
τεῦξε δέ οἱ κνημῖδας ἑανοῦ κασσιτέροιο.[10]
Translated as:
then wrought he for him acorselet brighter than the blaze of fire, and he wrought for him a heavy helmet, fitted to his temples, a fair helm, richly-dight, and set thereon a crest of gold; and he wrought himgreaves of pliant tin. But when the glorious god of the two strong arms had fashioned all the armour[11]
Liddell-Scott-Jones suggest the etymology to be originallyElamite; citing theBabyloniankassi-tira, hence thesanskritkastīram.[9] However theAkkadian word (thelingua franca of theAncient Near East, including Babylonia) for tin was "anna-ku"[12] (cuneiform: 𒀭𒈾[13]).Roman Ghirshman (1954) suggests, from the region of theKassites, an ancient people in west and centralIran; a view also taken by J D Muhly.[14] There are relatively few words inAncient Greek at begin with "κασσ-";[15] suggesting that it is anethnonym.[16] Attempts at understanding theetymology of the word were made inantiquity, such asPliny the Elder in hisHistoria Naturalis (book 34 chapter 37.1):
"White lead (tin) is the most valuable; the Greeks applied to it the namecassheros".[17]
AndStephanus of Byzantium in hisEthnica states:
"Κασσίτερα νησοσ εν τω Ωκεανω, τηΊνδικη προσεχης, ως Διονυσιοσ εν Βασσαρικοισ. Εξ ης οκασσίτερος."[16]
Which can be translated as:
Kassitera, an island in theocean, neighbouringIndia, asDionysius states in theBassarika. From there comestin.
It may be primarily used as a raw material fortin extraction and smelting.
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