THE MINERAL LEADHILLITE

• Chemistry: Pb₄SO₄(CO₃)₂(OH)₂ , Lead Sulfate Carbonate Hydroxide.
• Class: Carbonates
• Uses: Only as mineral specimens.
• Specimens

Leadhillite is an attractive, brightly lustered and sometimes colorful mineral that is often associated with other rare and beautiful oxidation minerals. Its list of associated minerals reads like a collectors wishlist. Leadhillite is named after its aptly named type locality of Leadhills, Lanarkshire, Strathclyde, Scotland. It forms in the oxidation zone of lead deposits as a secondary mineral, sometimes pseudomorphing other lead minerals and sometimes being pseudomorphed by other lead minerals. A pseudomorph is a mineral that has replaced either the structure or chemistry of an earlier mineral, without distorting the outward shape of the original mineral; thereby producing a crystal that has the shape of one mineral, but is actually either chemically and/or structurally a different mineral. Platy or tabular pseudohexagonal cyclic twinned crystals of leadhillite are the typical habit as well as prismatic crystals. The best specimens have come from Mammoth Mine, Tiger, Arizona. Leadhillite is trimorphous with the minerals macphersonite and susannite. Trimorphs are three different minerals that share the same chemistry, but have different structures. Leadhillite can be quite a popular collection mineral if it were only more available on the mineral markets.

PHYSICAL CHARACTERISTICS:

• Color is colorless, white, sky blue, pale sea green, yellow and gray. Color usually fades toward the center of the crystals.
• Luster is resinous to adamantine. Cleavage surfaces are pearly.
• Transparency: Crystals are transparent to translucent.
• Crystal System is monoclinic; 2/m.
• Crystal Habits include prismatic and tabular or platy crystals; also massive and granular. Pseudohexagonal and pseudorhombohedral twinned crystals are most common and Artini Law twins produce contact twinning. Larger crystals may have a concave basal face. Pseudomorphs after susannite are also seen. Leadhillite is also pseudomorphed by cerussite at times.
• Cleavage is perfect in one direction (basal) and poor in another.
• Fracture is conchoidal.
• Hardness is 2.5 - 3
• Specific Gravity is 6.3 - 6.6 (very heavy for a translucent mineral)
• Streak is white.
• Other Characteristics Some specimens are fluorescent orange.
• Associated Minerals include malachite, silver, willemite, susannite, wulfenite, dioptase, chalcocite, galena, caledonite, anglesite, linarite and cerussite.
• Notable Occurrences include the type locality at Leadhills, Lanarkshire, Strathclyde and at other localities in Scotland and at the Campbell Mine, Cochise County; the Grand Reef Mine, Graham County; the Rowley Mine, Maricopa County and the Mammoth-Anthony Mine, Tiger, Pinal County, Arizona; several mines such as the Cerro Gordo Mine in Inyo County and the Blue Bell Mine, San Diego County, California; Coeur D'Alene Mining District, Idaho and Granby, Missouri, USA; Langesundsfjord, Norway and Tsumeb, Namibia.
• Best Field Indicators: Crystal habit, color, luster, environment of formation, density and an almost micaceous cleavage.