Mineral 1

ACC Standard Mineral 10 - Amphibole, by Sean C Murphy 2020.

Specimen dimensions: 3 x 2 x 1½ inches (75x50x40mm)

Specimen weight: 11 ounces (314 grams)

Collection: Round Rock Campus


For reference: the U.S. penny is 0.75 inches [19.05 mm] in diameter.

Distinguishing Properties (click this to reveal) - make your list of observations before peeking

  • Cleavage - Look at this specimen closely, even though it is unevenly broken, one imagine a cross section with 6 sides (a hexagon) - find the mineral surfaces, this mineral has cleavage planes at every 60 and 120 degrees

  • Color: notice that this is a very dark-colored mineral (usually varieties are black, or possibly very dark green)

  • Hardness: this mineral is relatively hard and can scratch glass (5-6 on Moh's scale)

  • Note: Unfortunately, this mineral is very easily confused with pyroxene minerals that exhibit the same hardness and dark coloration. It is distinguished from pyroxenes by cleavage angles - pyroxene mineral surfaces/cleavage planes are almost 90 degrees (square shape). And different varieties of this mineral are so similar in appearance that often they can only be distinguished from one another by examination under an optical microscope. This mineral is an important component of many intermediate igneous and metamorphic rocks.