Plumbogummite
Plumbogummite is a rare secondary lead phosphate mineral, belonging to the alunite supergroup of minerals, crandallite subgroup. Some other members of this subgroup are:
- Crandallite, CaAl3(PO4)2(OH)5·H2O, where calcium replaces lead
- Goyazite, SrAl3(PO4)2(OH)5·H2O, where strontium replaces lead
- Philipsbornite, PbAl3(AsO4)2(OH)5·H2O, where the arsenate group AsO4 replaces the phosphate group PO4
| Plumbogummite | |
|---|---|
| General | |
| Category | Phosphate minerals |
| Formula (repeating unit) | PbAl3(PO4)2(OH)5·H2O |
| IMA symbol | Pbg |
| Strunz classification | 8.BL.10 |
| Dana classification | 42.7.3.5 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) |
| Space group | R3m |
| Identification | |
| Formula mass | 581.14 g/mol |
| Color | Blue, grey, greenish or yellow |
| Crystal habit | Crystals, rare, have a hexagonal outline |
| Cleavage | None |
| Fracture | Uneven or sub-conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 4 to 5 or 4.5 to 5 |
| Luster | Resinous or dull |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 4.014 |
| Optical properties | Uniaxial (+), segments of crystals may be biaxial |
| Refractive index | no = 1.653 or 1.653 to 1.688 ne = 1.675 or 1.675 to 1.704 |
| Pleochroism | None |
| Solubility | Soluble in hot acids |
| Other characteristics | Non-fluorescent, not radioactive |
| References | |
Plumbogummite was discovered in 1819 and named in 1832 from the Latin "plumbum" for lead, and "gummi" for gum, in allusion to its lead content and appearance, which at times resembles coatings of gum.
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