Here's the breakdown:
* Rock type: Boulders can be made of any type of rock:
* Igneous: Formed from cooled and solidified magma or lava (like granite, basalt, obsidian)
* Sedimentary: Formed from layers of sediment compressed and cemented together (like sandstone, limestone, shale)
* Metamorphic: Formed from existing rocks transformed by heat, pressure, or fluids (like marble, slate, gneiss)
* Composition: The specific composition of a boulder depends on the rock type. For example:
* Granite is made of quartz, feldspar, and mica.
* Limestone is primarily composed of calcium carbonate.
* Basalt is made of various minerals, including pyroxene, olivine, and plagioclase feldspar.
It's important to note that the size of a rock is what determines whether it's classified as a boulder. Generally, boulders are defined as rocks larger than 256 millimeters (10 inches) in diameter.
