| 词条 | Polyhalite |
| 释义 |
| name = Polyhalite | boxwidth = | boxbgcolor = | image = History museum of Truskavets 081.jpg | imagesize = | alt = | caption = Museum specimen of polyhalite and anhydrite | category = Sulfate mineral | formula = K2Ca2Mg(SO4)4·2H2O | molweight = | strunz = 7.CC.65 | dana = | system = Triclinic | class = Pinacoidal ({{overline|1}}) (same H-M symbol) | symmetry = F{{overline|1}} | unit cell = a = 6.95 Å, b = 8.88 Å, c = 6.95 Å; α = 104.06°, β = 113.94°, γ = 101.15°; Z = 4 | color = Colorless, white, gray; often salmon-pink to brick-red from included iron oxide | colour = | habit = Typically fibrous, foliated, massive; rarely as tabular crystals; pseudo-orthorhombic | twinning = Characteristically polysynthetic on {010}, {100} | cleavage = Perfect on {10{{overline|1}}}; parting on {010} | fracture = Conchoidal | tenacity = Brittle | mohs = 3.5 | luster = Vitreous to resinous | streak = White | diaphaneity = Transparent | gravity = 2.78 | density = | polish = | opticalprop = Biaxial (-) | refractive = nα = 1.546 - 1.548 nβ = 1.558 - 1.562 nγ = 1.567 | birefringence = δ = 0.021 | pleochroism = | 2V = Measured: 60° to 62° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = Soluble in water, with precipitation of gypsum and perhaps syngenite | impurities = | alteration = | other = | references = [1][2][3] }} Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: K2Ca2Mg(SO4)4·2H2O. Polyhalite crystallizes in the triclinic system, although crystals are very rare. The normal habit is massive to fibrous. It is typically colorless, white to gray, although it may be brick red due to iron oxide inclusions. It has a Mohs hardness of 3.5 and a specific gravity of 2.8. It occurs in sedimentary marine evaporites and is a major potassium ore mineral in the Carlsbad deposits of New Mexico. It is also present as a 2–3% contaminant of Himalayan salt. Polyhalite was first described in 1818 for specimens from its type locality in Salzburg, Austria.[1] The name comes from the German Polyhalit, which comes from the Ancient Greek words {{IPA|πολύς}} (polys) and {{IPA|ἅλς}} (hals), which mean "many" and "salt", and the German ending -it (which comes from the Latin ending -ites, which originally also came from Greek), which is used like the English ending -ite to form the names of certain chemical compounds.[4][3] Despite the similarity in names between halite (the naturally occurring form of table salt) and it, their only connection is that both are evaporite minerals. The use of the Greek words for many and salt in polyhalite is due to polyhalite consisting of several metals that can form salts in the more general sense of the word salt used in chemistry. ProductionThe only polyhalite mined in the world comes from a layer of rock over {{convert|1000|m|ft|abbr=on}} below the North Sea off the North Yorkshire coast in the UK. Deposited 260 million years ago, it lies {{convert|150-170|m|ft|abbr=on}} below the potash seam at the Boulby Mine. In 2010, the first mining operations of the polyhalite mineral commenced at Boulby Mine, the mine is currently the only producer of polyhalite which is marketed by Israel Chemicals Ltd as polysulphate. In 2016, Sirius Minerals plc announced plans for a new polyhalite mine in the area.[5] Composition and usePolyhalite is used as a fertilizer since it contains four important nutrients and is low in chloride:
References1. ^1 Polyhalite on Mindat.org 2. ^Polyhalite data on Webmin 3. ^1 Handbook of Mineralogy 4. ^[https://en.oxforddictionaries.com/definition/polyhalite] 5. ^{{cite web|last1=Topf|first1=Andrew|title=Banks backstop Sirius Minerals for $2.9B UK potash mine|url=http://www.mining.com/banks-backstop-sirius-minerals-2-9b-uk-potash-mine/|website=mining.com|date=1 September 2016|accessdate=1 December 2016}} 7 : Magnesium minerals|Calcium minerals|Potassium minerals|Sulfate minerals|Triclinic minerals|Evaporite|Potash |
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