1. Mineral Fragments: These are pieces of pre-existing rocks that have been broken down by weathering and erosion. They come in many forms, from sand grains to pebbles to larger boulders. Common minerals found in these fragments include quartz, feldspar, mica, and calcite.
2. Organic Remains: These are the remnants of once-living organisms. This can include:
* Plant Material: Fossils of leaves, stems, wood, or even pollen.
* Animal Remains: Bones, shells, teeth, or even whole skeletons.
* Organic Matter: Decomposed plant or animal matter, which contributes to the formation of coal or oil shale.
3. Chemical Precipitates: These are minerals that have crystallized directly out of water solutions. Examples include:
* Halite (rock salt): Forms when seawater evaporates.
* Gypsum: Also forms from evaporating water.
* Calcite: Can precipitate out of both fresh and saltwater.
It's important to note that these categories are not mutually exclusive. You might find a rock containing a mixture of all three types!
