Color and Pleochroism. Color and any change in color intensity on rotation of the stage. Color is related to chemical composition. Pleochroism is often diagnostic.

Habit, Shape or Outline. Habit can be diagnostic for euhedral grains. The shape of weathered or worn grains may also provide information on their nature, source, mode of transport, or type of weathering regime.

Size. Size seldom gives information on the nature of themineral, but may be important for interpretations of origin, mode of transport, or changes inlithology.

Cleavage. Principle and subordinate directions as well as patterns. Cleavage is a diagnostic characteristic of many minerals: micas (parallel), pyroxenes (cleavage planes intersecting at about 90°), amphiboles (two sets intersecting at about 120°). Due to physical and chemical weathering, cleavage planes may be obsured.

Fracture. Types of fracture (curved or uneven) and their position in the mineral. Olivines are characterized by an irregular cracking pattern, often showing alteration or weathering products.

Refractive Index and Relief. Absolute determination is difficult to impossible in thin-section, unless the grain orientation is known and the grain is surrounded by embedding media of known refractive index.

Inclusions, Intergrowths and Altereations. Inclusions are characteristic in some minerals (especially quartz) and may be useful in certain studies. However, they are of little pedogenic importance. Intergrowths and alteration products may indicate mineral weathering.

This page (http://www.ces.ncsu.edu/plymouth/programs/.html) created by
Vera MacConnell, Research Technician, I on November 17, 1997.
Last Updated on November 17, 1997.