Mellite

Organic mineral
2+1⁄2LusterVitreous, resinous, greasyStreakWhiteDiaphaneityTransparent to translucentSpecific gravity1.64Optical propertiesUniaxial (-) may be anomalously biaxialRefractive indexnω = 1.539 nε = 1.511Birefringenceδ = 0.028PleochroismWeak; O = yellowish brown; E = yellowUltraviolet fluorescencePale yellow to blue (LW & SW UV)Other characteristicsPyroelectricReferences[2][3][4]

Mellite, also called honeystone, is an unusual mineral being also an organic chemical. It is chemically identified as an aluminium salt of mellitic acid, and specifically as aluminium benzenehexacarboxylate hexadecahydrate, with the chemical formula Al2C6(COO)6·16H2O.[4]

It is a translucent honey-coloured crystal which can be polished and faceted to form striking gemstones. It crystallizes in the tetragonal system and occurs both in good crystals and as formless masses. It is soft with a Mohs hardness of 2 to 2.5 and has a low specific gravity of 1.6.[2][4]

It was discovered originally in 1789 at Artern in Thuringia, Germany. It has subsequently also been found in Russia, Austria, the Czech Republic, and Hungary. It was named from the Greek μέλι meli "honey",[5] in allusion to its color.[3]

It is found associated with lignite and is assumed to be formed from plant material with aluminium derived from clay.[2]

Cut and polished mellite gemstone

Structure

The crystal structure of mellite has been determined by neutron diffraction and consists of slightly distorted Al(H2O)63+ octahedra linked by hydrogen bonds to [C6(COO)6]6− mellitate anions and water of crystallization.[6]

See also

References

Wikimedia Commons has media related to Mellite.
  1. ^ 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. S2CID 235729616.
  2. ^ a b c http://rruff.geo.arizona.edu/doclib/hom/mellite.pdf Handbook of Mineralogy
  3. ^ a b "Mellite".
  4. ^ a b c http://webmineral.com/data/Mellite.shtml Webmineral data
  5. ^ μέλι. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
  6. ^ Robl, Christian; Kuhs, Werner F. (1991). "A neutron diffraction study on hydrogen bonding in the mineral mellite (Al2[C6(COO)6] · 16H2O) at 15 K". J. Solid State Chem. 92 (1): 101–109. Bibcode:1991JSSCh..92..101R. doi:10.1016/0022-4596(91)90246-E.


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