What is a Mesocratic rock?
Mesocratic —applied to rocks composed of approximately equal proportions of light-colored and dark-colored minerals; color index 30–60. Mesocrystalline —refers to a rock or rock texture in which the sizes of individual crystals are between those of a macrocrystalline and a microcrystalline rock.
What are melanocratic minerals?
Applied to dark-colored rocks, esp. igneous rocks, containing between 60% and 100% dark minerals; i.e., rocks, the color index of which is between 60 and 100.
What is melanocratic in geology?
Definition of melanocratic of igneous rock. : having predominantly dark mineral constituents — compare leucocratic, mesocratic.
What are Leucocratic minerals?
Definition of leucocratic of a mineral or rock. : having a light color — compare melanocratic, mesocratic.
How is Holocrystalline formed?
If the cooling period is long enough to let the atoms form orderly patterns and mineral crystals fully grow, the rock then has minerals with large particle size and crystal shape, which can be seen by eyes or low-magnification microscope. In this case, the rock is known as “holocrystalline”.
What are aphanitic igneous rocks?
Aphanitic rock is igneous rock in which the grain or crystalline structure is too fine to be seen by the unaided eye. Such rock is formed when the material solidifies at or near the surface so that the cooling is rather rapid. Such rocks are termed “extrusive” rocks.
What is holocrystalline rock?
Definition of holocrystalline : completely crystalline : made up wholly of crystals or crystalline particles —used of a rock (as granite)
What is holocrystalline texture?
Said of the texture of an igneous rock composed entirely of crystals, i.e., having no glassy part. Also, said of a rock with such a texture.
How is holocrystalline formed?
How is Glomeroporphyritic texture formed?
They generally form when magma that has been slowly cooling for a long time, possibly in a magma chamber, is suddenly erupted to Earth’s surface.
What is synonym of Glomeroporphyritic texture?
phenocryst texture … this is observed, the term glomeroporphyritic is used to describe the texture, and the aggregate is referred to as a glomerocryst.
What does mesocratic mean in geology?
Definition of mesocratic. of igneous rock. : having nearly equal dark and light mineral constituents a mesocratic diorite — compare leucocratic, melanocratic.
…minerals are said to be melanocratic. These terms can be applied to the rocks, depending on the relative proportion of each type of mineral present. In this regard, the term colour index, which refers to the total percentage of the rock occupied by mafic minerals, is useful.
What minerals are found in iron metamorphic rocks?
When ironstones and iron formations are metamorphosed, they quickly lose any original hydrous minerals. But any of the other original minerals may persist. At the lowest grades of metamorphism, magnetite and hematite most commonly dominate. If the original rock was rich in carbonate, siderite will be present.
What minerals are found in all grades of rocks?
Quartz and Na-rich plagioclase are in rocks of all grades. Kaolinite, pyrophyllite and chloritoid may also be present at low grade but are less common and are omitted from this figure. There is a great deal of overlap and many of these minerals exist together.