1. Igneous Rocks:
* Formation: Formed from the cooling and solidification of molten rock (magma or lava).
* Texture:
* Crystalline: Composed of interlocking mineral crystals, visible to the naked eye (e.g., granite).
* Glassy: Rapid cooling forms a non-crystalline structure (e.g., obsidian).
* Porphyritic: Large crystals embedded in a finer-grained matrix (e.g., porphyry).
* Composition: Varies widely depending on the type of magma or lava, but common minerals include quartz, feldspar, mica, and pyroxene.
* Examples: Granite, basalt, rhyolite, obsidian, pumice.
2. Sedimentary Rocks:
* Formation: Formed by the accumulation, cementation, and compaction of sediments (rock fragments, mineral grains, organic matter).
* Texture:
* Clastic: Composed of fragments derived from other rocks (e.g., sandstone).
* Chemical: Formed by precipitation of minerals from solution (e.g., limestone).
* Organic: Composed of organic matter, such as plant or animal remains (e.g., coal).
* Composition: Highly variable, depending on the source of the sediments.
* Examples: Sandstone, limestone, shale, coal, conglomerate.
3. Metamorphic Rocks:
* Formation: Formed from existing igneous, sedimentary, or even other metamorphic rocks by transformation due to heat, pressure, or chemical reactions.
* Texture:
* Foliated: Minerals are arranged in parallel layers (e.g., schist).
* Non-foliated: Minerals are randomly oriented (e.g., marble).
* Composition: Same chemical composition as the original rock, but minerals may be rearranged or altered.
* Examples: Marble, slate, gneiss, quartzite, schist.
Here's a table summarizing the key characteristics:
| Feature | Igneous | Sedimentary | Metamorphic |
|---|---|---|---|
| Formation | Cooling of magma or lava | Accumulation and cementation of sediments | Transformation of existing rocks by heat, pressure, or chemical reactions |
| Texture | Crystalline, glassy, porphyritic | Clastic, chemical, organic | Foliated, non-foliated |
| Composition | Highly variable | Highly variable | Same as original rock, but minerals may be altered |
| Examples | Granite, basalt, rhyolite, obsidian, pumice | Sandstone, limestone, shale, coal, conglomerate | Marble, slate, gneiss, quartzite, schist |
Remember that these are just general characteristics. There is significant variation within each rock type.
