See hollandite.

See hollandite.

A dioctahedral member of the brittle mica group. The end-member formula is: CaAl₂vAl₂Si₂O₁₀(OH)2, where v = vacancy. Typical site substitutions include: Ca > Na,K; v > Li; ^ivAl ≈ Si; ^ivAl > Be. Margarite is a rock-forming mineral and occurs in low- and medium-grade metamorphic rocks and at nearly all pressure grades. In addition, margarite commonly occurs as pseudomorphs, indicating retrograde reactions and/or polymetamorphism. Margarite most commonly is a 2M₁ polytype and, less often, as 1M and 1M_d. Tetrahedral site occupancies alternate with Si and Al around the tetrahedral ring, thereby producing a non-centric structure in space group Cc.
Cf., bityite

An obsolete term for muscovite.

An obsolete term for muscovite.

An obsolete term for chromian phengite and chromian muscovite.

An unconsolidated, soft sediment primarily composed of calcium carbonate, lime, and/or clay; impurities are common. Marl is formed in marine and lake deposits as a mud. Marl is used as a fertilizer to enhance calcium content and as a component of Portland cement.

An obsolete varietal term for a thinly foliated form of green-white serpentine.

An obsolete term for Mn-bearing glauconite from the Urals.

An obsolete term for glauconite.