This blog is about igneous rocks as I was researching Amazonite and found that I know very little about rocks and minerals.
Igneous rocks form from the solidification of molten rock material. There are two types of igneous rocks: intrusive and extrusive. The word, "igneous" is derived from the Latin word, 'ignis', meaning fire.
Intrusive Rocks are crystallized magma under the earth's surface that slowly pushes upwards, filling any cracks or spaces it can find. (This process takes millions of years to complete.) As the rock slowly cools into a solid, different parts of the magma crystallize into minerals.
• Diorite:
is a coarse-grained rock that contains feldspar, pyroxene and hornblende, plus sometimes it also contains quartz.
• Gabbro:
is also coarse-grained, along with being dark in color and contains feldspar, pyroxene, and sometimes it also has olivine.
• Granite:
is coarse-grained as well, but is light colored and is comprised mostly of quartz.
• Pegmatite:
is extremely coarse-grained and forms near margins of magma chambers, during the final stages of crystallization in the magma chamber. Pegmatite is composed of rare minerals (such as: microcline) that are not found in any other parts of the magma chamber.
A magma chamber is a large underground pool of liquid rock beneath the earth's surface. This molten rock is under great pressure and given enough time, this pressure can gradually fracture the rock around it causing a volcanic eruption.
• Peridotite:
Extrusive Rocks form when hot magma from inside the earth flows out onto surfaces as lava, or explodes violently into the atmosphere to fall back as pyroclastics or tuff. The main effect is that the magma cools quickly in open air or in seawater with very little to no growth of crystallization.
• Andesite:
is fine-grained and comprised mostly of plagioclase with other minerals (hornblende, pyroxene and biotite.)
• Basalt:
is also fine-grained but dark in color and is composed of plagioclase and pyroxene.
• Obsidian:
is dark colored volcanic glass formed from the very rapid cooling of molten rock material, with absolutely no form of crystallization.
• Pumice:
is light in color and has a vesicular texture which is caused by gas trapped in the melt at time of rapid solidification.
• Rhyolite:
is also lightly colored and fine-grained, typically contains quartz and feldspar materials.
Fire Opal can be found in cavities of rhyolite. Long after rhyolite cools, silica-rich groundwater moves through the rock depositing gems like opal, red beryl, topaz, jasper or agate.
• Scoria:
is dark in color and also has a vesicular texture that often forms a frothy crust on top of lava flow or as material ejected from a volcanic vent and solidifies while airborne.
• Tuff:
is composed of materials ejected from a volcano, fell to the earth and then lithified into rock. It is composed of mostly volcanic ash and sometimes contains cinders and other large-sized materials.
The other two types of rocks are:
• Sedimentary
• Metamorphic
#IgneousRocka #IgneousRock #Geology #IntrusiveRocks #ExtrusiveRocks
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