isoclinic

Isoclinic is an adjective used primarily in crystallography and mineral optics to describe a relation involving equal inclination of certain crystallographic directions with respect to a reference plane or direction. The term comes from Greek roots meaning equal slope or angle.

In the context of biaxial crystals, which possess two optic axes, isoclinic describes planes or sections in which the optic axes intersect the plane or direction at equal angles. This concept helps describe how light propagates through the crystal and is used in optical orientation work. Isoclinic lines or isoclinic sections are tools for interpreting optical properties, often in conjunction with polarized light microscopy and conoscopic interference figures. They assist in determining the crystal’s optic orientation and the refractive index parameters.

Isoclinic, isogonic, and related terms appear in the terminology of mineral optics to distinguish different geometric relationships of optic axes, planes, and propagation directions. Isoclinic lines are contrasted with other diagnostic features such as isogyres (lines associated with dark interference figures) and isogons (directions of equal optical rotation). Together, these concepts form part of the practical framework used to analyze and identify minerals based on their optical behavior.

Outside of mineral optics, the term isoclinic can be encountered less formally to indicate any situation where two directions or lines maintain equal angular relations to a reference plane or axis, though this usage is far less standardized. In proper scientific contexts, the mineral-optics sense is the canonical one.