Grain Size

Image credit: James St. John

Grain Size

In this simplified treatment, observation of grain size is made without magnification (e.g., hand lens, microscope). However, digital assets may be imaged and enlarged on a computer display. So a physical examination of the grain size of a hand sample of an unknown rock may not provide as much detail as on a computer display.

An assessment of grain size, whether viewed by hand sample or computer display, remains the same - a judgment is made about the visibility and sizes of grains (crystals).

• coarse-grained - particles that are larger than a grain of sand (approximately)
• medium-grained - particles that are still visible individually yet somewhat smaller than a grain of sand (approximately)
• fine-grained - particles that individually invisible - too small to be individually resolved

Here are examples for training (calibrating) your eye and mind.