Mellite should not be confused with Melilite.
| Mellite | |
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| Category: | Organic minerals |
| Formula: | Al2[C<sub>6</sub>(COO)<sub>6</sub>]·16H2O |
| Imasymbol: | Mel[1] |
| Strunz: | 10.AC.05 |
| System: | Tetragonal |
| Class: | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
| Symmetry: | I41/acd |
| Unit Cell: | a = 15.53 Å, c = 23.19 Å; Z = 8 |
| Color: | Honey-yellow, deep red, pale shades of red, brown, gray, white; |
| Habit: | Elongated bipyramidal prismatic; as nodules and coatings, fine-grained massive |
| Cleavage: | poor/indistinct on |
| Fracture: | conchoidal |
| Tenacity: | Slightly sectile |
| Mohs: | 2- |
| Luster: | Vitreous, resinous, greasy |
| Streak: | White |
| Diaphaneity: | Transparent to translucent |
| Gravity: | 1.64 |
| Opticalprop: | Uniaxial (-) may be anomalously biaxial |
| Refractive: | nω = 1.539 nε = 1.511 |
| Birefringence: | δ = 0.028 |
| Pleochroism: | Weak; O = yellowish brown; E = yellow |
| Fluorescence: | Pale yellow to blue (LW & SW UV) |
| Other: | Pyroelectric |
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.[2]
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.[3] [2]
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 Greek, Ancient (to 1453);: μέλι meli "honey",[4] in allusion to its color.[5]
It is found associated with lignite and is assumed to be formed from plant material with aluminium derived from clay.[3]
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 [C<sub>6</sub>(COO)<sub>6</sub>]6− mellitate anions and water of crystallization.[6]