LEADHILLITE

    Class : Carbonates, nitrates, borates
    Subclass : Anhydrous carbonates
    Crystal system : Monoclinic
    Chemistry : Pb4(SO4)(CO3)2(OH)2
    Rarity : Uncommon

Leadhillite is a secondary carbonate from the oxidation zone of lead deposits, mixed with other secondary lead, zinc or copper minerals (anglesite, aurichalcite, cerussite, linarite, etc...). It is also found in certain industrial slags. It owes its name to its locality of discovery : Leadhills (Scotland). Leadhillite occurs in tabular pseudohexagonal prisms, thin or thick, with perfect cleavage according to (001), or in almost sectile grained masses. transparent to translucent, resinous to adamantine luster, leadhillite is white to gray, yellowish, sometimes green, blue-green or colorless. Like many lead minerals, leadhillite is characterized by a high density (over 6.5).

Main photo : Leadhillite from Mammoth-Saint Anthony Mine, Arizona, USA © Mark Mauthner

10 cm leadhillite and cerussite from Tsumeb, Namibia © Jeffrey Scovil
Leadhillite from Leadhills, South Lanarkshire, Scotland © Rock Currier
Leadhillite from Clara Mine, Germany © Volker Heck
Leadhillite from Poullaouen slag, Finistère, France © Pascal Chollet

Leadhillite in the World

Beautiful specimens come from the type locality of Leadhills (Scotland), which produced magnificent 2 cm green-yellow tabular crystals in the 19th century. But the largest known crystals come from Tsumeb (Namibia) where thick, gray tabular crystals measuring up to 15 cm by 5 cm were discovered. Stunning blue crystals are known from the Mammoth St-Anthony Mine (Arizona), while the Tiny Mine near Iglesias (Sardinia, Italy) has also yielded beautiful crystals. Leadhillite is also of high quality in the Moroccan mine of Touissit, near Oujda.

Leadhillite in France

In France, leadhillite is known in good centimeter-sized crystals at the Argentolle mine (Saône-et-Loire). It is reported in Propière, Beaujeu and Lantignié (Rhône), in Kaymar (Aveyron), in Urbeis (Bas-Rhin) and in the slag of Poullaouen (Finistère) and Crozet (Loire).

Twinning

Leadhillite commonly twins on {140}; in the form of lamellar twins with the composition plane parallel to {-142} or {340} ; as an aragonite-type contact twin producing pseudohexagonal groups.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2.5 to 3
Density : 6.55
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.870 to 2.010
Birefringence : 0.140
Optical character : Biaxial -
Pleochroism : None
Fluorescence : Pale yellow

Solubility : Hot water, nitric acid

Magnetism : NoneRadioactivity : None