The solid lithospheric crust beneath our feet is a colossal storehouse of rocks. Geochemists establish that approximately 98% of the crust consists of just eight elemental building blocks (Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, and Magnesium). These elements combine to form minerals, which aggregate into rocks.
Definitions of Minerals & Rocks
A mineral is a naturally occurring, homogeneous inorganic chemical substance with an orderly internal crystalline lattice. A rock is an aggregate composed of one or more minerals forming the solid lithosphere.
Monomineralic vs Polymineralic Rocks
Rocks composed of a single mineral species are termed monomineralic (e.g., pure Limestone composed of calcite $\text{CaCO}_3$). Polymineralic rocks comprise multiple minerals (e.g., Granite comprising quartz, feldspar, and mica).
Igneous Rocks: Primary Progenitors
Formed through the cooling and consolidation of molten subterranean magma or surface lava. Characterized by interlocking crystals, high density, and a complete absence of fossils.
Sedimentary Rocks: Layered Strata
Forged through the denudation of older rocks, transport by rivers and wind, and layered sedimentation in aquatic basins. These are the only rocks containing true fossils (জীবাশ্ম).
Metamorphic Rocks: Recrystallized Stones
Formed when pre-existing rocks undergo profound mineralogical and textural recrystallization under subterranean temperatures ($200^\circ-800^\circ\text{C}$) and crushing lithostatic stress.