A dioctahedral member of the true mica group. The end-member formula is NaAl₂vAlSi₃O₁₀(OH)₂, where v = vacancy, and thus paragonite is the Na analogue of muscovite. The typical range in composition is: K < 0.5, Ca ≤ 0.11. (Rieder et al., 1998). Paragonite occurs as 2M₁, 3T, and 1M polytypes. Paragonite is found in low- and medium-grade metapelites and at variable pressures near those of greenschist and blueschist facies. It commonly occurs with muscovite/phengite and margarite.
Cf., muscovite.

A weak magnetic attraction that develops in the presence of an external magnetic field and this attraction occurs when magnetic moments align in the material. When the magnetic field is removed, the magnetic moments (thermally) randomize and the magnetic behavior disappears. Paramagnetism is found in substances with atoms/molecules possessing an odd number of unpaired electrons. Hence, transition metals with partly filled 3d orbital electronic shells may show paramagnetic behavior. Thus, metals (e.g., Ti) and compounds (e.g., fayalite, augite, annite) may be paramagnetic.
Cf., magnetic susceptibility

Hydrated clays mixed with paraffin, heated to 40-45

A modulated 2:1 layer silicate with continuous Mn-rich octahedral sheets and 6-fold tetrahedral rings forming islands three rings wide. These islands have inter-island linkages, some of which have inverted tetrahedra, involving 12-fold tetrahedral rings and double four-member rings, which act to link adjacent tetrahedral sheets (Eggleton and Guggenheim, 1994). A structural formula for parsettensite is M_7.5(Mn,Mg)₄₉(Si_64.5Al_7.5)_Σ=72O₁₆₈(OH)₅₀ ^. nH₂O. Parsettensite occurs in (low grade to very low grade) metasedimentary manganese ore deposits in Val d’Err, Oberhalbstein, Graubünden, Switzerland and on surfaces of pegmatite minerals by either hydrothermal or pneumatalytic processes at the Foote mine, Kings Mountain, North Carolina, USA, and in a very low grade metagraywacke and argillite near Otago, New Zealand.
Cf., stilpnomelane

A mechanical property where a mineral breaks along a planar or near-planar structural weakness. Parting usually results from plane-like defects, often twinning, or is produced by anisotropic stress. In contrast, cleavage is a property of the periodic crystal structure.
Cf., cleavage

An obsolete term for the Fe-free variety of bixbyite, alpha-(Fe,Mn)₂O₃.

A poorly defined material, possibly interstratified biotite and vermiculite.

An obsolete term for trilithionite.

An obsolete term for margarite.

Having a luster similar to that of mother-of-pearl with an interplay of rainbow-like colors (iridescent).