Granite is an igneous rock formed from magma that intrudes into the Earth's crust. It is classified based on the percentages of quartz, alkali feldspar, and plagioclase feldspar. True granite contains both plagioclase and alkali feldspars. Chemically, granite is composed largely of silica, alumina, potassium, and sodium. Granite occurs globally in continental crust and forms much of the basement rock beneath sedimentary layers.

2. Mineralogy:
 Granite is classified according to the
QAPE diagram for coarse grained
plutonic rocks and is named according
to the percentage of quartz, alkali
feldspar (orthoclase,sanidine, or
microline) and plagioclase feldspar on
the A-Q-P half of the diagram.

3. Mineralogy II:
True granite according to modern
petrologic convention contains
both plagioclase and alkali
feldspars.

4. Origin:
 Granite is an igneous rock and is formed
from magma. Granitic magma has many
potential origins but it must intrude other
rocks. Most granite intrusions are emplaced
at depth within the crust, usually greater
than 1.5 kilometers and up to 50 km depth
within thick continental crust.

5. Origin II:
 The origin of granite is contentious and has led to
varied schemes of classification. Classification
schemes are regional and include French, British,
and American systems.

6. Chemical composition:
 A worldwide average of the chemical composition of granite, by
weight percent:
 SIO — 72.04% (silica)
 AIO — 14.42% (alumina)
 K2O — 4.12%
 NA2O — 3.69%
 CaO — 1.82%
 FeO— 1.68%
 Fe2O3 — 1.22%
 MgO — 0.71%
 TIO3— 0.30%
 P2O5 — 0.12%
 MnO — 0.05%

7. Occurrence:
 Granite is currently known only on Earth, where it
forms a major part of continental crust. Granite
often occurs as relatively small, less than 100 km²
stock masses (stocks) and in bathilotis that are
often associated with orogenic mountain ranges.
Small dikesof granitic composition called aplites
are often associated with the margins of granitic
intrusions. In some locations, very coarse-grained
pegmatite masses occur with granite.

8. Occurence II:
 Granite has been intruded into the crust of the
Earth during all geologic periods, although much
of it is of Precambrian age. Granitic rock is widely
distributed throughout the continental crust and
is the most abundant basement rock that underlies
the relatively thin sedimentary veneer of the
continents.

9. Geochemical origins:
 Granitoids are a ubiquitous component of the
crust. They have crystallized from magmas that
have compositions at or near a eutetic point (or a
temperature minimum on a cotectic curve).

10. Geochemical origins II:
 Magmas will evolve to the eutectic because of
igneous differentation, or because they represent
low degrees of partial melting.fractional
crystallysation serves to reduce a melt in
iron,magnesium, titanium, calcium and sodium,
and enrich the melt in potassium and silicon -
alkali feldspar (rich in potassium) and quartz
(SiO2), are two of the defining constituents of
granite.

11. PHOTOS