Leadhillite
Leadhillite is a lead sulfate carbonate closely linked to and trimorphous with Susannite and Macphersonite. Trimorphs are three different minerals that share the chemistry that is same but have various crystal structures. In this complete case, Leadhillite is monoclinic, Susannite is trigonal and Macphersonite is orthorhombic. Leadhillite is most usually found as small to microscopic clear to tabular that is white crystals but also can be found in bigger sizes, to 13 cm, as prismatic crystals and in various shades of yellow, green, blue and brown. Leadhillite is fairly soft having a Mohs hardness of just 2.5, however, a relatively high certain gravity of 6.26 to 6.55 and resinous to the luster that is adamantine. Leadhillite was called in 1832 after the kind locality, Susanna mine, Leadhills, Lanarkshire, Scotland. A number of the most useful specimens have resulted from the Mammoth Mine, Tiger, Arizona. Attractive specimens are not rare but certainly not common but gems which are faceted extremely uncommon.
Distribution: In Scotland, from Leadhills, Lanarkshire, and Wanlockhead, Dumfriesshire; into the Drumruck mine, Kirkcudbrightshire. In England, from Caldbeck Fells, Cumbria; at Penberthy Croft, St. Hilary, and into the Greystone quarry, Levant, Cornwall. From Bleiberg, Carinthia, Austria. In America, through the Beer Cellar mine, Granby, Newton County, Missouri; in the Tintic district, Juab County, Utah; in Arizona, fine crystals from the Mammoth-St. Anthony mine, Tiger, Pinal County, in the Rowley Mine, near Theba, Maricopa County, during the Grand Reef mine, Gila County, and from Bisbee, Cochise County. In California, at the Blue Bell claims, near Baker, San Bernardino County; from the Searchlight district, Clark County, plus in the Chalk Mountain mine, Chalk hill district, Churchill County, Nevada; from Leadville, Lake County, Colorado. Very crystals that are large Tsumeb, Namibia. At Dundas, Tasmania, Australia. A few other localities are known.
| Category: | Carbonate minerals |
| Chemical Formula: | Pb4(SO4)(SO3)2(OH)2 |
| Lead Sulfate Carbonate Hydroxide | |
| Molecular Weight: | 1,078.90 gm |
| Composition: | Hydrogen | 0.19 % | H | 1.67 % | H2O |
| Lead | 78.82 % | Pb | 88.68 % | PbO2 | |
| Carbon | 2.23 % | C | 8.16 % | CO2 | |
| Sulfur | 2.97 % | S | 7.42 % | SO3 | |
| Oxygen | 17.80 % | O | |||
| 100.00 % | 105.93 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals, to 13 cm, are usually thin to thick tabular pseudohexagonal, with hexagonal outline; several rhombohedral and pyramidal forms common; may be barrel-shaped, or pseudorhombohedral {101} and {142}, also prismatic parallel to [001], or equant, granular or massive. When [101] is developed the faces may show striations, or be curved. Over 40 forms noted; granular, massive. |
| Twinning: | On {140}, {340}, {140}, very common, giving pseudohexagonal groupings. |
| Cleavage: | Perfect on {001} and easy. Parting: translation gliding on {001}, as well as twin gliding with K1(340), σ2[140]; K2(34¯0), σ1[140]. |
| Fracture: | Irregular/Uneven |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.5 – 3.0 |
| Density: | 6.55 (g/cm3) |
| Luminescence: | Pale yellowish under Short Wave UV |
| Radioactivity: | Not Radioactive |
| Thermal Behaviour: | Heating results in a reversible transformation into Susannite. 2E is approximately 20° (2V ~ 10°) at ambient temperature (for Na) and decreases with increasing temperature. It becomes uniaxial negative at about 125° and remains so at higher temperatures. |
| Other: | Soluble in nitric acid with effervescence, rendering a residue of lead sulphate. Exfoliates in hot water. |
| Health Warning: | Caution: Contains lead – always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. |
| Color: | Colorless, white, gray, pale yellow, yellow, yellowish green, pale green, pale bluish green, pale blue, brown; colorless in transmitted light |
| Transparency: | Transparent to translucent |
| Luster: | Resinous to adamantine, pearly on {001} |
| Refractive Index: | 1.870 – 2.010 Biaxial ( – ) |
| Birefringence: | 0.140 |
| Dispersion: | Strong; r < v |
| Pleochroism: | n/a |
