prize9-2, Exercise 1: A glassy grey mineral

Model answer (check the details):

Tests used: lustre (glassy), hardness (scratches glass, so harder than about 5.5), and the acid test (no fizz, so not calcite).

Most likely: quartz, which is glassy, about 7 on the Mohs scale, and does not react with acid.

Confidence: fairly good, but not certain. Other hard glassy minerals exist (some feldspars are about 6), so check fracture (quartz breaks in curved surfaces, feldspar in flat cleavage planes) and, if possible, a streak test (white).

Care: say "most likely" and name the extra test that would settle it.