melanocratic

melanocratic

[¦mel·ə·nō¦krad·ik]
(geology)
Dark-colored, referring to igneous rock containing at least 50-60% mafic minerals. Also known as chromocratic; melanic.
References in periodicals archive ?
It is either massive or has a gneissic banding formed by alternating leucocratic and amphibole-bearing melanocratic layers.
The clinopyroxene-bearing albitite and its melanocratic layers show replacement to rutile-bearing, light pink, fine-grained albitite.
2a), and subsidiary phases of medium-grained equigranular granite, equigranular to quartz-feldspar-phyric microgranite, melanocratic biotite granite, and minor aplite and pegmatite (MacLellan et al.
Leucocratic (gneisses, granites, migmatites) and melanocratic (amphibolites, schists, metagabbro) rocks differ clearly in the values of p.
Petrographically gabbroic rocks are melanocratic, holocrystalline, medium to coarse grained and subpoilikitic in texture.
Hornblende-rich gabbro is melanocratic, holocrystalline, medium to coarse grained and subporphyritic in texture (Fig.
The rock exposures occur as highly denuded hills of essentially fine-medium textures with closely spaced alternating bands of leucocratic and melanocratic minerals.
Lithologic varieties observed in the stock include a compositional range from tonalites to monzogranite, with enclaves of melanocratic diorites (Fig.
Ultrabasic rocks--metaperidotites, serpentinites, and melanocratic amphibolites--are described only in four drill cores, where they form veins of different thickness inside the basic rocks.
The rocks of the Strazek Moldanubicum are penetrated with smaller postmetamorphic gabbro bodies; further with melanocratic granites and even syenites (durbachites) abounding in potassium and with two-mica granites.
The comparatively lower [Fe.sub.2][O.sub.3] values in the quartz schist are due to the almost total absence of melanocratic minerals.
The chemical variability combined with textural features such as the occurrence of melanocratic and leucocratic layering (Blackwood 1991) suggests that many of the analyzed samples represent crystal cumulates, rather than magma compositions.

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