Everything about Diorite totally explained
Diorite is a grey to dark grey intermediate
intrusive igneous rock composed principally of
plagioclase feldspar (typically
andesine),
biotite,
hornblende, and/or
pyroxene. It may contain small amounts of
quartz,
microcline and
olivine.
Zircon,
apatite,
sphene,
magnetite,
ilmenite and
sulfides occur as accessory
minerals. It can also be black or bluish-grey, and frequently has a greenish cast. Varieties deficient in hornblende and other dark minerals are called
leucodiorite. When
olivine and more
iron-rich
augite are present, the rock grades into ferrodiorite, which is transitional to
gabbro. The presence of significant quartz makes the rock type quartz-diorite (>5% quartz) or
tonalite (>20% quartz), and if
orthoclase (
potassium feldspar) is present at greater than ten percent the rock type grades into
monzodiorite or
granodiorite.
Diorites may be associated with either
granite or
gabbro intrusions, into which they may subtly merge. Diorite results from partial melting of a
mafic rock above a
subduction zone. It is commonly produced in
volcanic arcs, and in cordilleran
mountain building such as in the
Andes Mountains as large
batholiths. The
extrusive volcanic equivalent rock type is
andesite.
Historic use of diorite
Diorite is an extremely hard rock, making it difficult to carve and work with. It is so hard that ancient civilizations (such as
Ancient Egypt) used diorite balls to work granite. Its hardness, however, also allows it to be worked finely and take a high polish, and to provide a durable finished work. Thus, major works in diorite tend to be important.
One comparatively frequent use of diorite was for inscription, as it's easier to carve in relief than in three-dimensional
statuary. Perhaps the most famous diorite work extant is the
Code of Hammurabi, inscribed upon a 2 metre (7 ft) pillar of black diorite. The original can be seen today in Paris' Musée de
Louvre. A few large statues remain, including several statues of King Khafre in the Egyptian Museum. The use of diorite in art was most important among very early Middle Eastern civilizations such as
Ancient Egypt,
Babylonia,
Assyria and
Sumer. It was so valued in early times that the first great
Mesopotamian empire -- the Empire of
Sargon of
Akkad -- listed the taking of diorite as a purpose of military expeditions.
Although one can find diorite art from later periods, it became more popular as a structural stone and was frequently used as pavement due to its durability. Diorite was used by both the
Inca and
Mayan civilizations, but mostly for fortress walls, weaponry, etc. It was especially popular with medieval Islamic builders. In later times, diorite was commonly used as cobblestone; today many diorite cobblestone streets can be found in England, Guernsey and Scotland, and scattered throughout the world in such places as Ecuador and China. Although diorite is rough-textured in nature, its ability to take a polish can be seen in the diorite steps of
St. Paul's Cathedral, London, where centuries of foot traffic have polished the steps to a sheen.
Occurrence
Diorite is a relatively rare rock; source localities include
Sondrio,
Italy;
Thuringia and
Saxony in
Germany;
Finland;
Romania; Northeastern
Turkey; central
Sweden;
Scotland; the Darrans range of
New Zealand; the Andes Mountains; the Isle of
Guernsey; and the
Basin and Range province and
Minnesota in the
USA.
An
orbicular variety found in
Corsica is called
corsite.
Further Information
Get more info on 'Diorite'.
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