SHANDITE
Shandite – Ni3Pb2S2 – is a very rare sulfide. It is of no importance as an ore, even though it contains 26.90% Ni and 63.31% Pb by weight.
It may contain Zn, Fe, Mn, and Co.
1. Characteristics
Crystal system: Trigonal scalenohedral.
Color: Brass yellow.
Habit: It occurs as tiny, rounded grains. It can be pseudocubic.
Cleavage: {1011} perfect.
Tenacity: No information available.
Twinning: No.
Fracture: No information available.
Mohs Hardness: 4
Parting: No.
Streak: No information available.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 8.72
2. Geology and Deposits
At the type locality (Tasmania, Australia), it occurs in serpentinites, generally as inclusions within other minerals.
In other occurrences (Greenland), it forms segregations within an Fe-rich lens hosted in basalt.
Shandite has been identified at only about twenty five localities worldwide (2026).
3. Mineral Associations
At the type locality, shandite almost always occurs in oriented intergrowths with heazlewoodite (Ni3S2). It can also form crusts on other sulfides. At this locality, it occurs with chromite, magnetite, sphalerite, pentlandite, and serpentine (lizardite).
At the Greenland (Denmark) occurrence, it is associated with native iron, native lead, galena, altaite, and troilite.
At the Jeffrey Mine (Canada), it is associated with colorless garnet (grossular) and green chromian garnet.
4. Transmitted Light Microscopy
Not applicable, as shandite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: Shandite easily takes on an excellent-quality polish.
PLANE POLARIZED LIGHT – PPL
Reflection color: Light creamy white, or white with a subtle cream undertone.
Pleochroism: Distinct.
Reflectivity: ~40%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Very strong anisotropy between blue-gray and yellow-brown.
Internal reflections: No.
May be confused with: A few other minerals, considering the paragenesis is important. Identifying shandite is relatively straightforward when considering Ni ore minerals.
Heazlewoodite exhibits very similar pleochroism.
Parkerite occurs only in pyrrhotite-related Ni deposits.
General Characteristics:
Grain shape: generally rounded. When occurring as lamellae, they are oriented parallel to the (0001) plane of heazlewoodite.
Cleavage of shandite extends in the same orientation into the host mineral, heazlewoodite.
Replacement of shandite by heazlewoodite may occur.
Inclusions: small lamellar inclusions of sphalerite, oriented parallel to the (0001) plane of shandite, are present in some cases.
