DUFTITE

Duftite – PbCu(AsO₄)(OH) – is a rare arsenate, one of the many secondary minerals that make up oxidized ores from polymetallic deposits, in this case of Cu and Pb.
It belongs to the Adelite-Desclozite Group and has calcium-duftite and β-duftite as varieties.

1. Characteristics

Crystal system: Orthorhombic bisphenoidal.

Color: Olive green, grey-green.

Habit: Generally massive, botryoidal or in crusts.
Rare elongated pseudo-octahedral crystals [001], with curved and rough faces.

Cleavage: Indistinct.

Tenacity: Brittle.

Twinning: No.

Fracture: Conchoidal

Mohs Hardness: 4.5

Parting: No.

Streak: Pale green, white.

Lustre: Vitreous in fractures. Dull on faces.

Diaphaneity: Transparent.

Density (g/cm³): 6.12

2. Geology and Deposits

Duftite occurs as a secondary mineral in the oxidized zones of some polymetallic sulfide deposits. It is not a common mineral and is difficult to recognize in the complex and multicolored assemblage of secondary minerals in this type of deposit.

There are at least a dozen secondary Cu minerals – among the most common – that exhibit green colors in various shades: malachite, pseudomalachite, dioptase, botallackite, atacamite, paratacamite, antlerite, brochantite, natrocalcite, and libethenite.

3. Mineral Associations

It is associated with typical gangue minerals such as quartz, carbonates (calcite, dolomite) and adamite.
It occurs with secondary Cu minerals such as azurite, bayldonite, malachite, mottramite, olivenite, dioptase and rosasite.

In addition, with secondary Pb minerals such as bayldonite, beudantite, cerussite, mimetite, mottramite and wulfenite.

4. Transmitted Light Microscopy

Refraction indices: n_α: 2.030 – 2.040 n_β: 2.060 – 2.080 n_γ: 2.080 – 2.100

PLANE POLARIZED LIGHT – PPL

Color / Pleochroism: Light apple green, without pleochroism.

Relief: Very high.

Cleavage: No.

Habits: Botryoidal, crusts.

CROSSED POLARIZED LIGHT – XPL

Birefringence and Interference Colors: Maximum birefringence of 0.050 to 0.060, very high, with interference colors up to the end of the 3rd order: intense, colorful.

Extinction: Paralell to the form.

Elongation sign: No information available.

Twins: No.

Zoning: Common due to compositional variations.

CONVERGENT LIGHT

Character: B(-)

2V angle: No information available.

Alterations: It does not alters, it is a product of alteration.

May be confused with: other green secondary copper minerals.

5. Reflected Light Microscopy

Sample preparation: no information available.

PLANE POLARIZED LIGHT – PPL

Reflection color: Medium gray.

Pleochroism: No.

Reflectivity: ~15%

Bireflectance: No.

CROSSED POLARIZED LIGHT – XPL

Isotropy / Anisotropy: Anisotropy was not observed.

Internal reflections: Luminous light yellowish green.

May be confused with: other green transparent minerals.