How can you identify different types of rocks?
I’m studying fοr mу Junior Certificate аnd rіght now I’m revising rocks bυt I hаνе nο thουght hοw tο tеll thеm apart. Whаt dο thеу look lіkе?
I need Igneous, Sedimentary аnd Metamorphic.
If уου know ехсеllеnt websites еіthеr, mау possibly уου leave a link?
I already tryed friggin google!
try google?
Igneous:
http://geology.about.com/cs/basics_roxmin/a/aa011804a.htm
Sedimentary:
http://geology.about.com/cs/basics_roxmin/a/aa011804b.htm
Metamorphic:
http://geology.about.com/cs/basics_roxmin/a/aa011804c.htm
also use yahoo images search engine to see pictures, it might help.
Excellent Luck!
Igneous : These rocks are basically solidified lava. As such, they have small if any grain structure and the more solid kinds break like glass and have very sharp edges. Examples are obsidian and pumice.
Metamorphic: These rocks are typically surface sediments which get pushed under the crust. There, the heat and pressure of the mantle partially liquefies them. They save much of their grain structure, but the grains themselves are very tightly packed and somewhat fused together. Metamorphic rocks are also amongst the toughest of rocks because they have been compacted to such an extent. Metamorphic rocks contain granite and marble. Marble is what the sedimentary rock mineral becomes after heat and compression.
Sedimentary : these are mineralized deposits of surface material, usually either sand, mud or small shells and coral. This sediment becomes buried and compressed, but not to the extent that metamorphic rocks do. Because of this, sedimentary rocks have a very gritty structure and are the softest of rocks. Sedimentary rocks are where most fossils are found. Mineral itself is really a massive fossil consisting of millions of tiny shells of extinct nautical organisms. Besides mineral, there is shale which originated as mud and sandstone which was once sand.
Sand itself is a mineral called quartz. It is nearly pure silicon dioxide. Rocks are made up of several types of minerals. Geologists identify minerals and rocks according to hardness and the affect of the streak they leave when scratched. Other things used are density. granite is very dense, but pumice is filled with air spaces and is a rock which really floats.
It is a vast subject itself, called Petrology, and very trying to answer briefly.
Generally speaking, Igneous rocks are only primary source for all rocks. They can be extrusive like lava, hypabyssal like dolerites or Plutonic, like a granite. Plutonic rocks are all coarse grained, Hypabyssal rocks are standard grained and volcanic rocks are fine grained. They are characteristically crystalline, i.e., a mass of interlocking crystalline minerals.
Sedimentary rocks are trying to recognize. Generally they show some sedimentary reputation like a bedding plane. Moreover, there is no interlocking crystalline reputation in them.
A metamorphic rock usally show predictable metamorphic texture like a gneissosity or a schistosity or a slaty cleavage. They also host one or more metamorphic index minerals like garnet, chlorite, kyanite, andalusite, sillimanite etc.
But there are thousands of rock types and their distinguishing feature are so variable, it is generally impossible to describe a common feature or two in them. For example, Grannite can be a plutonic igneous rock, or a sedimentary granite (product of the process called granitisation) or metamorphic (granite gneiss). It is practically very trying to distinguish a Quartzite (metamorphic) from an Orthoquartzite (sedimentary).
Best process of identifying a rock is to identify its minerals constituents and study its texture, both in hand-specimen and under microspcope.
Roger S : Obsidian and pumice are rather minor components of igneous rocks of the world. Major rocks like granite, basalt, gabbro, alkali rocks, mafic-ultramafics etc – all these have definte crystal grains.
And Sand in geology refers to a particular grain size and not quartz.