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The name diorite (from Ancient Greek διορίζειν, "to distinguish") was first applied to the rock by René Just Haüy [10] on account of its characteristic, easily identifiable large crystals of hornblende. [4] Dioritoids form a family of rock types similar to diorite, such as monzodiorite, quartz diorite, or nepheline-bearing diorite ...
The way a mineral splits (or “cleaves”), particularly along planes in the crystal structure. Cleavage is generally described by. how well a mineral can be split to produce a flat plane, a process controlled by planes of weakness in the crystal structure. the number of distinct directions of these cleavage planes; the angles between those ...
Polished slab; blue color is labradorescence. Since they are primarily composed of plagioclase feldspar, most of Proterozoic anorthosites appear, in outcrop , to be grey or bluish. Individual plagioclase crystals may be black, white, blue, or grey, and may exhibit an iridescence known as labradorescence on fresh surfaces.
Napoleonite is a variety of diorite which is characterized by orbicular structure. The grey matrix of the stone has the normal appearance of a diorite, but contains many rounded lumps 1 or 2 inches in diameter, which show concentric zones of light and dark colors.
The name comes from two related rocks to which granodiorite is an intermediate: granite and diorite. The gran-root comes from the Latin grānum for "grain", an English language derivative. Diorite is named after the contrasting colors of the rock.
Hornblende has a hardness of 5–6, a specific gravity of 3.0 to 3.6, and is typically an opaque green, dark green, brown, or black color. It tends to form slender prismatic to bladed crystals, diamond-shaped in cross section, or is present as irregular grains or fibrous masses. [7] Its planes of cleavage intersect at 56° and 124° angles.
Graph of komatiite geochemistry MgO% vs Cr ppm, from basal flows, Wannaway, Western Australia. The pristine volcanic mineralogy of komatiites is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian pyroxene, anorthite (An85 and upwards) and chromite.
In hand specimen, many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, and black crystals of biotite and hornblende. Other dacites, especially pyroxene-bearing dacites, are darker colored. [4] In thin section, dacites may have an aphanitic to porphyritic texture.