Minerals and Igneous Rocks

A comprehensive set of flashcards covering key concepts, minerals, and characteristics related to igneous rocks, derived from the lecture notes.

Muscovite mica

Thin clear sheets.

Biotite mica

Thin greenish/black sheets.

Plagioclase feldspar

Shiller (pearlescent luster) and straight laminae.

Pyrite

Brassy color with cubic crystals.

Orthoclase feldspar

Typically has a salmon color and wavy lamellae.

Amphibole (Hornblende)

Sheety, elongate, but NOT prismatic and appears fibrous.

Garnet

Dodecahedral crystals.

Graphite

Soft, gray streak with a metallic luster.

Gypsum

Fibrous texture, often clear or white, with three cleavage planes(one distinctive).

Halite

Salty taste, perfectly cubic crystals, and often rounded edges.

Calcite

Rhombohedral crystals with double refraction. Reacts to HCL

Copper

Metallic luster and tarnishes blue/green.

Galena

Metallic luster, cubic shape, and dense.

Talc

Pearly luster and very soft.

Hematite specular

Glittery metallic luster with a red streak.

Quartz

Hard, glassy, and can be used to make a tool.

Augite (Pyroxene)

Green tint with a 90-degree cleavage.

Felsic rocks

•Light colored

•Mostly composed of quartz and feldspars

•Most common mafic mineral in felsic rocks is biotite mica

Mafic rocks

Dark colored

Mostly composed of pyroxene

Ultramafic rocks have olivine

Rich in magnesium and iron

Intrusive rocks

Cool slowly at depth, allowing crystals to grow; typically exhibit phaneritic texture.

Extrusive rocks

Cool quickly at the surface; may exhibit glassy or vesicular texture.

Phaneritic texture

Characterized by visible crystals to the naked eye, matching intrusive rocks.

Porphyritic texture

Indicates a dual cooling history; primarily associated with extrusive rocks, exhibiting larger crystals in a finer matrix.

Glassy texture

Lava cools so quickly that crystals can’t nucleate, typically found in extrusive rocks, characterized by conchoidal fracture.

Vesicular texture

Significant number of holes left from escaping gases, typically associated with extrusive rocks.

Pegmatitic texture

Coarse-grained texture characterized by crystal size > 2.5 cm; commonly felsic.

Pyroclastic texture

Lavas produced by explosive volcanic eruptions; associated with extrusive rocks.

Olivine

Green, glassy, granular

Hematite oolitic

Reddish color

Red streak

Aphanitic Texture

Crystals are not visible to the naked eye

May feel gritty to the touch

Gabbro

An intrusive, phaneritic, mafic igneous rock.

Diorite

An intrusive, phaneritic, intermediate igneous rock.

Granite

An intrusive, phaneritic, felsic igneous rock, typically pink or white.

Basalt

An extrusive, aphanitic, mafic igneous rock.

Rhyolite

An extrusive, aphanitic, felsic igneous rock.

Obsidian

An extrusive, glassy igneous rock that cannot reveal composition from color.

Scoria

An extrusive, vesicular rock that is intermediate or mafic.

Pumice

An extrusive, vesicular, felsic rock.

Peridotite

An intrusive, phaneritic ultramafic rock, primarily composed of olivine.