THE MINERAL ARTHURITE
- Chemistry: CuFe2(AsO4, PO4, SO4)2 – 4H2O, Hydrated Copper Iron Arsenate Phosphate Sulfate Hydroxide
- Class: PhosphateClass
- Subclass: Arsenates
- Group: Arthurite
- Uses: Only as mineral specimens.
Arthurite is a rare copper iron arsenate. It is typically green and forms small acicular crystals. Specimens from the classic mines of Cornwall, England are often associated with other rare minerals such as pharmacosiderite and beudantite, and these specimens are much sought after. Arthurite is unusual in that it contains a variety of anions, namely arsenate, phosphate and sulfate. Percentage whys, the arsenate anion dominates in natural specimens, but all anions are usually present in the same specimen.
Arthurite lends its name to a small group of rather obscure minerals called the Arthurite Group. The Arthurite Group is a group of monoclinic, hydrated iron arsenates and phosphates with a general formula of XFe2(AO4)2(O, OH)2 – 2H2O The X in the formula can be either copper, iron, manganese and/or zinc. The A in the formula can be either arsenic or phosphorous.
These are the members of the Arthurite Group:
- Arthurite (Hydrated Copper Iron Arsenate Phosphate Sulfate Hydroxide)
- Earlshannonite (Hydrated Manganese Iron Phosphate Hydroxide)
- Ojuelaite (Hydrated Zinc Iron Arsenate Hydroxide)
- Whitmoreite (Hydrated Iron Phosphate Hydroxide)
- Color is apple green to emerald green.
- Luster is vitreous to pearly.
- Transparency: Crystals are translucent.
- Crystal System is monoclinic.
- Crystal Habits include prismatic to acicular crystals and globular aggregates and crusts.
- Cleavage is not observed.
- Fracture is uneven.
- Hardness is 3 – 4
- Specific Gravity is approximately 3.0 – 3.2 (average for translucent minerals).
- Streak is green.
- Associated Minerals are pharmacosiderite, beudantite and other secondary arsenate minerals.
- Notable Occurrences include Calstock, Cornwall, England; Atacama Province, Chile and Majuba Hill, Nevada, USA.
- Best Field Indicators are color, crystal habit, streak and associations.