Rocks: Kinds of Igneous Rock

| November 6, 2009 | 26 Comments

Igneous rocks are made from lava or magma. Lava and magma are made of hot, melted minerals. Lava is found on or near the Earth’s surface. Magma is found far beneath the Earth’s surface.


Andesite is a kind of extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture.

clip_image002

Basalt is a common extrusive volcanic rock.  It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet.  It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey.

clip_image004

Dike is a planar wall rock structures, such as bedding or foliation.  massive rock formations, like igneous/magmatic intrusions and salt diapirs.Dikes can therefore be either intrusive or sedimentary in origin.

clip_image006

Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar 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

clip_image008

Dolerite is a mafic, holocrystalline, intrusive igneous rock equivalent to volcanic basalt or plutonic gabbro.

clip_image010 

Felsite is a very fine grained volcanic rock that may or may not contain larger crystals.  Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition

clip_image012

Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt.  The rocks are plutonic, formed when molten magma is trapped beneath the Earth’s surface and cools into a crystalline mass.

clip_image014

Granite is a common and widely occurring type of intrusive, felsic, igneous rock.  Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Outcrops of granite tend to form tors, and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.

clip_image016

Microdiorite is a medium-grained intrusive igneous rock.  It contains crystals that are smaller than grains of rice, which are interlocking and randomly oriented.  It is dark grey or greenish brown.

clip_image018

Microgranite is a medium-grained intrusive igneous rock.  It contains crystals, smaller than grains of rice, which are interlocking and randomly oriented.  It is pale grey and can sometimes be pinkish in colour.  It contains a number of minerals, mostly feldspars, which are pale grey or pinkish, and quartz, which is grey or white. It also contains small specs of mafic minerals.

clip_image020

Obsidian is a kind of igneous rock that form when lava cools quickly above ground. Obsidian is actually glass and not a mixture of minerals.  The edges of this rock are very sharp.

clip_image022

Pegmatite is a plutonic rock with exceptionally large crystals.  It forms at a late stage in the solidification of granite bodies.

clip_image024

Peridotite is a dark igneous rocks consisting mainly of olivine and other ferromagnesian minerals

clip_image026

Pitchstone is a dull black glassy volcanic rock formed when lava cools swiftly.

clip_image028

Pumice is a kind of igneous rock which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. This rock is so light, that many pumice rocks will actually float in water. Pumice is actually a kind of glass and not a mixture of minerals. Because this rock is so light, it is used quite often as a decorative landscape stone. Ground to a powder, it is used as an abrasive in polish compounds and in Lava soap.

clip_image030

Rhyolite has a composition similar to granite but has a much smaller grain size.  It is composed of the light-colored silicates and is usually buff to pink in color.  Occasionally it is light gray. In texture it is classified as aphanitic. It frequently contains voids and glassy fragments, evidence of having formed in a surface environment with rapid cooling.

clip_image032

Serpentinite is a kind of rock composed of one or more serpentine minerals.  Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth’s mantle. The alteration is particularly important at the sea floor at tectonic plate boundaries.

clip_image034

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts.

clip_image036

Trachyte a fine-grained, light-colored, extrusive igneous rock, consisting chiefly of alkali feldspars.  It is the extrusive equivalent to syenite.

clip_image038

Xenolith is a rock fragment which becomes enveloped in a larger rock during the latter’s development and hardening.

clip_image040

<< back      next >>

Tags: , , , , ,

Category: Earth Science

About the Author (Author Profile)

Comments (26)

Trackback URL | Comments RSS Feed

  1. bryan says:

    pa kanos a ka muuli

  2. kimverlie says:

    thankssssssssssss♥♥♥

  3. rachel says:

    tnxxxxx sabi kasi ni teacher mag searh kami tnx for this!!!!1

  4. rachel atencio says:

    sorry,tnxxxx sabi kasi ni teacher mag search kami tnxxx na nilagay po ito! muaaaahhhhh

  5. dianne says:

    thank u so much…………..lab yahhhh

  6. josephine says:

    the….”"” kainis nman anu bang
    klaseng ass. 2 hehe………its ok.

  7. jessa says:

    buti n lng merong ganito…hehe…thnx…

  8. jessa says:

    ang pangit nman ng pic ko

  9. annalie says:

    woo!!!!!!! this is so cool!!!!!!!!!!

  10. annalie says:

    jan.29,2011

  11. annalie says:

    plz…………….

  12. jave.. says:

    may isa pang rocks na ang tawag ay baracks
    kung saan na ka tira ang mga militar……
    jejejejejejejej

  13. nicole says:

    tnx………. buti meron nito kung wala lagot ako sa teacher ko joke hindi naman …………

  14. miara says:

    research sbi ni mam

  15. hazel says:

    hay salamat………………

  16. Gerald says:

    buti na lang meron nito kundi lahot ako sa teacher ko

  17. jhecelyn says:

    ..buti na lang meron nito kundi lahot ako sa teacher ko
    !!!!!!!

  18. yenyen says:

    salamat poh

  19. irvin ongyaco says:

    thank you so muchhhh….

Leave a Reply