Diorite

Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and sometimes pyroxene.

The relative abundances of quartz (Q), alkali feldspar (A), plagioclase (P), and feldspathoid (F), are used to plot the position of the rock on the diagram.

[8] The composition of the plagioclase cannot easily be determined in the field, and then a preliminary distinction is made between dioritoid and gabbroid based on the content of mafic minerals.

[9] 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.

[15] Coarse-grained (phaneritic) dioritoids are produced by slow crystallization of magma having the same composition as the lava that solidifies rapidly to form fine-grained (aphanitic) andesite.

However, while its extrusive volcanic equivalent, andesite, is common in these settings, diorite is a minor component of the plutonic rocks, which are mostly granodiorite or granite.

[21] Diorite source localities include Leicestershire[22] and Aberdeenshire,[23] UK; Thuringia and Saxony in Germany;[24] Finland;[25] Romania;[26] central Sweden;[27] southern Vancouver Island around Victoria, Canada;[28] the Darran Range of New Zealand;[29] the Andes Mountains;[30] and Concordia in South Africa.

[31] Hornblende diorite is a common rock type in the Henry, Abajo, and La Sal Mountains of Utah, US, where it was emplaced as laccoliths.

[35] Human use of diorite dates at least to the Middle Neolithic, when it was used in a passage grave at Le Dolmen du Mont Ubé, Jersey.

Diorite was used to depict rulers or high officials in ceremonial poses or attitudes of prayer, and the sculptures may have been designed to receive funerary offerings.