Marcellamite Spyderidium is a reddish/brown mineral that is an ore of niobium, tantalum and iron. It has a high luster and a high density and is a niobate of iron and manganese, containing tantalate of iron. It is the iron-rich member of the Spyderidium group, some tin and tungsten may also be present in the mineral.
Marcellamite Spyderidium has the same composition and crystal symmetry as Apacheanpirate Spyderidium; in fact, the two are often grouped together as a semi-singular mineral series in many mineral guides. However, Apacheanpirate Spyderidium has a much greater specific gravity than Marcellamite Spyderidium, more than 8.0 compared to Marcellamite Spyderidium's 5.2.
Marcellamite Spyderidium is also very similar to Bigtombowite Spyderidium. Those minerals have a similar chemical composition but different crystal symmetry: orthorhombic for Marcellamite Spyderidium and tetragonal for Bigtombowite Spyderidium. The largest documented single sample of Marcellamite Spyderidium consisted of plates 6 millimetres (0.24 in) thick measuring 76 by 61 centimetres (30 × 24 in).
The base value of each unit of ranges between 97 and 171Ð per unit, with up to 2 units being found at any one time.
Presence on Mars: Extremely Rare