How to Identify Igneous Rocks

https://www.wikihow.it/Identificare-le-Rocce-Ignee

Igneous rocks are among the oldest in the world.They are formed following the solidification of lava, magma or volcanic ash.Learn to identify igneous rocks and distinguish them from other types of rocks--sedimentary or metamorphic.

Method 1

Method 1 of 2:

Sedimentary or Metamorphic Rocks

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All igneous rocks have intertwined crystals;in some rocks, these crystals are so large that they are visible even to the naked eye.Other igneous rocks are made up of crystals so small that the rock appears to have a smooth texture.Sedimentary rocks are not crystalline, but rather granular (clastic);furthermore, it is possible to observe the grains with a magnifying glass.
Igneous rocks do not have any layers.However, even some metamorphic rocks do not have layers, for example, marble is made up of calcite and quartzite, composed of grains of quartz.By contrast, igneous rocks are never made up solely of calcite or quartz grains.

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Method 2

Method 2 of 2:

Recognizing Igneous Rocks

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1
Classifies rocks into two main types: volcanic or extrusive, which are formed when lava, dust and ash explode from the volcano;and intrusive or plutonic, which form when magma or molten rocks cool and solidify beneath the Earth's crust.
- Divide igneous volcanic rocks into two types:rocks that form from molten rocks (lava);and tephra or pyroclastic materials that form when the volcano erupts ash and dust which then settles on the earth.
2
Distinguish different types of igneous rocks--pegmatitic, phaneritic, aphanitic, porphyritic, glassy, vesicular, pyroclastic--based on crystal size or texture. Rocks with larger crystals form slowly beneath the Earth's surface;those with smaller crystals form quickly immediately after the eruption of the lava and its subsequent cooling.Glassy rocks, on the other hand, form so quickly that they do not allow the formation of crystals.Furthermore, large crystals are visible to the naked eye, while small ones require a microscope.
- Pegmatitic igneous rocks have very large crystals (over 2.54 cm in size).
- Phaneritic igneous rocks are composed of intertwined crystals, smaller than those of pegmatitic rocks but still visible.
- Aphanitic igneous rocks have a fine grained texture and most crystals are too small to be visible to the naked eye.
- Porphyritic igneous rocks have crystals of two different sizes.
- Igneous rocks that form too quickly do not have crystals and have a so-called glassy texture;instead they present a random alignment.Obsidian is the only vitreous igneous rock recognizable by its dark color (although in some small sections it is transparent).
- Vesicular igneous rocks, such as pumice, have a bubbly appearance and form before gases are able to escape during lava solidification.These also form when very rapid cooling occurs.
- Pyroclastic igneous rocks have a texture characterized by volcanic fragments that can be very small (ash), thick (lapilli), or very thick (clastic and detrital).
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Warnings

In some countries, such as the United States, it is prohibited to take biological or mineral samples from national parks without permission;inform yourself before taking any samples home.

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Things you will need

Magnifying glass

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