-
Composed wholly of crystals e.g. granite
Holocrystalline
-
Composed entirely of glass e.g. obsidian
Holohyaline
-
Composed of both glass and crystals e.g. lava, shallow obtrusive rocks
Hypocrystalline
-
If most constituents can't be seen by the naked eye, the rock has a _____ texture.
Aphanitic
-
Crystals can be distinguished by a microscope.
Microcrystalline
-
Crystals cannot be distinguished by a microscope.
Cryptocrystalline
-
If the crystals can be identified with a hand lens alone, the rock has a ______ texture.
Phaneritic
-
Fine-grained =
Average diameter of individual grains is less than or equal to 1mm
-
Medium-grained =
Average diameter of individual grains is 1-5mm
-
Coarse-grained =
Average diameter of individual grains is 5mm-3cm
-
Very coarse-grained =
Average diameter of individual grains is more than 3cm
-
Holocrystalline rocks of medium and coarse grain (e.g. granite) are typical of...
Plutonic intrusions. They crystallised slowly from magmas intruded at 800-1000 degrees Celsius and then cooled slowly.
-
Finely crystalline, aphanitic, and glassy textures are typical of...
Rapid cooling
-
Grains completely bound by rational (straight) crystal faces
Euhedral
-
Grains partly bounded by crystal faces
Subhedral
-
Grains devoid of crystal faces, often irregular shapes
Anhedral
-
Crystals all same size and shape
Equigranular
-
Some grains euhedral, some subhedral, and some anhedral crystals (granitic texture), mostly seen in granites.
Subhedral granular
-
Phenocrysts gathered in distinct clusters
Glomeroporphyritic
-
Intergrowth of crystals (e.g. feldspar and pyroxene)
Ophitic
-
Numerous minerals enclosed within crystals of different composition
Poikilitic
|
|
