Iron muscovite

An invalid name for a hypothetical end member.

Iron-sericite

An obsolete varietal term for ferrian illite.

Irvingite

An obsolete varietal term for lithian muscovite.

Isinglas

An obsolete term for muscovite.

Isomorphous

Isomorphous literally means “having the same form”. The idea was first described by F. Beudant around 1800 (see Zoltai and Stout, 1984, p. 5-6) to describe crystals having the same form but having compositions between FeSO4 and ZnSO4. Thus, the term subsequently became commonly used to describe a series of crystals having continuously varying composition even where crystal faces are lacking. Such homogeneous chemical mixtures display a continuous range of properties, e.g., from the Fe to Zn end members. Such a series of solids is referred to as an “isomorphous substitution” series (archaic) or “solid solution” series. See “solid solution” for additional discussion.
Isomorphic (syn)

isotropy

a description of material with physical properties that are the same regardless of direction of measurement. Cf., anisotropy

Isotropy

A description of material with physical properties that are the same regardless of direction of measurement.
Cf., anisotropy

Ivigtite

A poorly defined material, possibly muscovite or sodian ferruginous mica.

Jadeite

A pyroxene with chemical formula of NaAlSi2O6. Jadeite occurs in high-pressure, low temperature metamorphic rocks and is the primary mineral in jade.
See pyroxene group for additional details.

Jefferisite

An obsolete name for altered material, probably vermiculite.