THE MINERAL TSUMEBITE

• Chemistry: Pb2Cu(PO4)(SO4)OH , Lead Copper Phosphate Sulfate Hydroxide
• Class: Phosphates
• Uses: only as a mineral specimen.
• Specimens

Tsumebite forms good, colorful specimens and is a popular collection mineral, although quite rare. It is closely related to its cousin, arsentsumebite. The two minerals are in a series in which the arsenate ion group in arsentsumebite is replaced by a phosphate ion group in tsumebite. The two differ only slightly mostly because the structure is the same in the two minerals. Both are formed in the oxidation zone of lead-copper ore deposits.

Both minerals are unusual in that they have two ion groups instead of the usual one in most minerals. It the case of tsumebite, it has a phosphate ion group and a sulfate ion group. Mineralogists prefer to classify it as a phosphate because the phosphate ion group has a higher negative charge (-3) than the sulfate group (-2).

PHYSICAL CHARACTERISTICS:

• Color is emerald green and yellow-green.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System is monoclinic.
• Crystal Habits include tabular crystals that can form twinned trillings and also as crusts and spherules.
• Cleavage: None.
• Fracture: Uneven.
• Hardness is 3.5
• Specific Gravity is approximately 6.2 (heavy for translucent minerals)
• Streak is green.
• Associated Minerals include azurite, wulfenite, mimetite, cerussite and smithsonite.
• Notable Occurrences are limited to Tsumeb, Namibia and Morenci, Arizona, USA.
• Best Field Indicators are crystal habit, locality, associations, density and color.