Table of Contents
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 is Leucocratic?
Definition of leucocratic of a mineral or rock. : having a light color — compare melanocratic, mesocratic.
What is the percentage of dark minerals in Leucocratic rocks?
Igneous rocks are classified into 4 groups based on C.I.: leucocratic rocks: < 30% light minerals (C.I. < 30)
What is modal abundance?
Modal abundance is obtained by measuring the abundance of actual minerals. This is in contrast to normative abundance, which is obtained by computing presumed mineralogy based on chemical abundance. The mineral groups used are referred to as Q, A, P, F and M.
What does Holocrystalline mean?
completely crystalline
Definition of holocrystalline : completely crystalline : made up wholly of crystals or crystalline particles —used of a rock (as granite)
Can gabbro be magnetic?
Further, they concluded that • the gabbros have the stable magnetic polarity component of strength more than 1.6 A/m and • the gabbroic rocks contribute to 40% of the seafloor spreading magnetic anomalies.
What is a Mesocratic rock?
Definition of mesocratic of igneous rock. : having nearly equal dark and light mineral constituents a mesocratic diorite — compare leucocratic, melanocratic.
What is Intergrowth texture?
In petrology, micrographic texture is a fine-grained intergrowth of quartz and alkali feldspar, interpreted as the last product of crystallization in some igneous rocks which contain high or moderately high percentages of silica. Micropegmatite is an outmoded terminology for micrographic texture.
What are sialic rocks?
Definition of sialic : of, relating to, or being relatively light rock that is rich in silica and alumina and is typical of the outer layers of the earth.
What is Modal mineral?
Modal mineralogies vary considerably because of phase layering and the irregular distribution of minerals in the rock, but an average mode consists of ~60% plagioclase, 30% clinopyroxene, and 10% olivine, with trace amounts of orthopyroxene, opaque minerals, and amphibole (Table T1).
Is pumice a holocrystalline?
There are no fine-shaped crystals, the groundmass develop as volcanic glass (obsidian, pumice). The volcanic rocks are holocrystalline, hipocrystalline or glassy.
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”.
Where can I find gabbro?
Gabbro is a dense, mafic intrusive rock. It generally occurs as batholiths and laccoliths and is often found along mid-ocean ridges or in ancient mountains composed of compressed and uplifted oceanic crust.
Why are Komatiites rare on Earth’s surface today?
Komatiite is an exceedingly rare type of lava. No volcano on Earth erupts this material today. Komatiites are essentially restricted to the Archean (4.55 to 2.5 billion years ago), when Earth’s heat flux was much higher.
What is the equivalent of granite?
rhyolite
rhyolite, extrusive igneous rock that is the volcanic equivalent of granite.
What is a Vitrophyric texture?
Vitrophyric texture is porphyric texture with phenocrysts isolated in glassy matrix. Glassy and vitrophyric texture occur in volcanic rocks. Hemicrystalline texture (from Greek hemi– half) is diagnostic of rocks, in which crystallized minerals dominate over glass.
What is melanocratic igneous rock?
igneous rock. In igneous rock: Mineralogical components …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.
…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 is the Colour Index of a rock?
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.