THE MINERAL GRATONITE

• Chemistry: Pb9As4S15, Lead Arsenic Sulfide
• Class: Sulfides
• Subclass: Sulfosalts
• Uses: Mineral specimens and as a very minor ore of lead.
• Specimens

Gratonite is a rare lead sulfide mineral. It forms nice crystals that can be arranged into rosette-like clusters with projecting rhombohedral terminations. Clusters can be attractive and good specimens command large prices, mostly because of the rarity of the mineral. Gratonite is a sulfosalt, a segment of sulfides where the arsenic acts more like a metal than a non-metal and occupies a position where it is bonded to sulfurs.

Also, Gratonite is the most common mineral whose symmetry is in the Trigonal Pyramidal Class

PHYSICAL CHARACTERISTICS:

• Color is a dark lead gray.
• Luster is metallic.
• Transparency: Crystals are opaque.
• Crystal System: Trigonal; 3
• Crystal Habits include rhombohedral as well as hexagonal prismatic crystals capped by three rhombohedral faces. Clusters can be found in rosette-like aggregates, also massive.
• Cleavage: None.
• Fracture: Subconchoidal.
• Hardness is 2.5
• Specific Gravity is 6.2 (heavier than average for metallic minerals)
• Streak is gray.
• Notable Occurrences are limited to the Excelsior Mine, Cerro de Pasco, Peru.
• Best Field Indicators are crystal habit, locality, color and density.