Minerals and Rocks

UPSC frequently tests the relative abundance of elements in the Earth's crust (Oxygen is the most abundant at 46.6%, followed by Silicon, Aluminium, and Iron) versus the whole-Earth elemental abundance where Iron dominates. Candidates must master the Mohs scale of mineral hardness (ranging from Talc as 1 to Diamond as 10) and distinct physical properties like cleavage (tendency to break along definite planes) versus fracture (irregular, non-directional breakage). Do not skip the physical properties table as UPSC targets specific optical and structural criteria like luster, streak, and transparency.

This section forms the foundation for resource geography and classification questions such as the MMDR Act 1957 major versus minor mineral distinction tested in GS1-2020-92. Focus on specific mineral properties: Feldspar contains silicon and oxygen plus sodium, potassium, calcium, or aluminium and makes up half of the crust; Quartz is silica-insoluble and a major constituent of sand. Skip deep chemical structural formulas, but memorize mineral groupings (e.g., Olivine contains magnesium and iron, often found in basaltic rocks). Mica is highly used in electrical industries due to its dielectric strength, not just thermal insulation.

Extremely critical for conceptual questions on petrology. Memorize the division of Igneous rocks (plutonic vs volcanic, acidic vs basic) such as granite, gabbro, pegmatite, basalt. Understand Sedimentary rock classifications: mechanically formed (sandstone, conglomerate, shale, loess), organically formed (geyserite, chalk, limestone, coal), and chemically formed (chert, halite, potash). Metamorphic rocks require clear distinction between thermal (contact and regional) vs dynamic metamorphism, and structural changes like foliation, lineation, and banding. Basalt is fine-grained and extrusive, while Granite is coarse-grained and intrusive; confusing their cooling rates and crystal sizes is a classic UPSC trap.

The rock cycle represents a continuous geological process where old rocks are transformed into new ones. Weathering and erosion turn all rock types into sedimentary inputs, which is directly relevant to biogeochemical cycling where weathering of rocks (specifically phosphorus cycle, as in GS1-2021-27) releases critical nutrients. Focus on the transformation pathways (e.g., sedimentary rocks undergoing metamorphism, or direct melting of metamorphic rocks back into magma). Skip overextended geomorphic cycle theories here as they are covered in subsequent chapters.