Igneous Rock
Igneous rocks are formed from the cooling of magma (lat. 'igneous' = fire).
Molten rock turns into solid below the Earth's crust - intrusive igneous rocks or on the
Earth's surface - extrusive igneous rocks.
Structure
Association of the minerals within the rock according to: form, dimensions, cystalinity degree
etc
After crystalinity degree:
-holocrystaline (e.g. granite, granodiorite etc);
-hypocristalyne (ryolite, andesit etc);
-vitrous (e.g. obsidian, perlit etc).
After crystals dimensions:
-Granular;
-Porphyric (great cristals in groundmass).
Texture
Spatial distribution and minerals` arrangement.
-massive;
-fluidale;
-scoriacee/vacuolar.
Magmatic rocks classification after consolidation place:
Intrusive: formed in the Earths`depth;
Extrusive: resulting from extrusion of molten material (magma) at the surface of the Earth
(lava) and its consolitdation there.
* Price, M., Walsh, K., (2010), Roci și minerale, Editura Litera, București
Magmatic Rocks Classification
Granite Familly
Granite* - pink to gray in color depending on mineralogical compozition, intrusive, acid;
structure granular, texture phaneritic. Mineral components: quartz (20% quartz by
volume),mica, feldspar etc. The average density of granite is between 2.65-2.75 g/cm3,
Melting temperature is cca 1215 -1260 °C.
Rhyolite -volcanic rock, extrusive,felsic > 69% SiO2. It may have any texture from glassy to
to porphyritic. The mineral composition is usually quartz, alkali feldspar and plagioclase,
biotite and hornblende.
Obsidian
Perlit
Granodiorite Familly
Granodiorite is an intrusive plutonic rock, very similar to granite, > 20% Quartz by volume,
cca 65% of the feldspar. It usually contains abundant biotite mica and hornblende, giving it a
darker appearance.
Dacite* - volcanic rock; porphyritic structure and is intermediate in composition between
andesite and rhyolite.
Sienite Familly
Sienite* is plutonic rock intermedie, brown-grey, quarz (<5%), containing a great quantity
of feldspar, amphiboli, mica, biotite,apatite, titanite etc The structure is granulare, and the
texture porphyric.
Trahit* it is a volcanic rock (SiO2 57,6 - 69 %) . Mineralogical composition remarque Oxides
alcaline Sodium and Potassium; over 7 %, feldspar (9 0%), quartz 10 și 20 %,
pyroxene, blenda, biotite etc.
Familly Diorite
Diorite* – intermediate intrusive rock composed principally of feldspar, biotite,hornblende,
pyroxene. Is a grey to dark grey of quartz, olivine. Zircon, apatite, sphene,magnetite, etc
Andesite* is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic
to porphyritic structure. (SiO2) it ranges from 57 to 63%.The mineral assemblage is typically
dominated by plagioclase, pyroxene and/hornblende, magnetite,zircon, apatite, biotite etc
* Price, M., Walsh, K., (2010), Roci și minerale, Editura Litera, București
Gabbrou Familly
Gabbro* - dark, coarse-grained, intrusive rocks. The vast majority of the Earth's surface is
underlain by gabbro within the oceanic crust, produced by basalt magmatism at mid-ocean
ridges. Contains pyroxene, feldspar plagioclase,amphibole, olivine, iron-titanium oxides etc
Basalt* common extrusive igneous rock formed from the rapid cooling of
basaltic lava exposed at or very near the surface. By definition, basalt must be
an aphanitic igneous rock with less than 20% quartz and less than 10% feldspathoid by
volume, and where at least 65% of the feldspar. Basalt is usually grey to black in colour.
Basalt with a vesicular or frothy texture is called scoria.
Peridotit Familly
Peridotite* is coarse-grained igneous rock, consisting mostly of the minerals olivine and
pyroxene, contains less than 45% silica. Peridotite is derived from the Earth's mantle. Picrit
Picrite, extrusive volcanic rock, represented by mixes of olivine titanium-
rich augite pyroxene with minor plagioclase set in a groundmass made of augite and
plagioclase, biotite etc.
Selective Bibliography
Anastasiu, N., Mutihac, V., Grigorescu, D., Popescu, Gh., (1998), Dicţionar de Geologie, Ed.
Didactică şi Pedagogică, Bucureşti.
Carmichael, Ian S. E., Turner, Francis J., and Verhoogen, John; (1974) Igneous Petrology,
McGraw-Hill, pp. 406 – 426.
Ciobanu, Rodica., (2005), Geologie generala. Indrumator pentru lucrarile practice. Editura
Universitatii ``Lucian Blaga``, Sibiu.
Cotet, P., (1971), Geomorfologie cu elemente de geologie, Ed. Didactica si Pedagogica,
Bucuresti
Le Maitre, L.E., ed., (2002) Igneous Rocks: A Classification and Glossary of Terms 2nd
edition, Cambridge.
Hyndman, Donald W. (1985). Petrology of igneous and metamorphic rocks (2nd ed. ed.).
McGraw-Hill. ISBN 0-07-031658-9.
Hamilton, W., Wolley, A., R., Bishop, A., (1979), The Hamlyn guide to Minerals, Rocks and
Fossils, London.
Ilieş C. Dorina (2000), Geologie generală – lucrări practice, Oradea.
http://www.besafenet.net/
https://www.rocksforkids.com/igneous-rock/
* Price, M., Walsh, K., (2010), Roci și minerale, Editura Litera, București
