Notes on Sedimentary and Metamorphic Rocks

Sedimentary Rocks and Their Metamorphosed Forms

  • Sedimentary sandstones are commonly dominated by grains of the mineral quartz.

    • Upon metamorphism, the quartz sand grains undergo

    • Recrystallization: The sand grains recrystallize and grow.

    • This process results in a non-foliated mass of interlocking quartz crystals, referred to as quartzite.

    • Properties of quartzite:

    • Primarily composed of quartz, thus sharing properties with the mineral.

    • Exhibits resistance to chemical weathering.

    • Has the ability to easily scratch glass, indicating its hardness.

  • Sedimentary limestone is dominantly composed of the mineral calcite.

    • When metamorphosed, the calcite bioclasts undergo

    • Recrystallization: The calcite in the limestone recrystallizes and grows.

    • This forms a non-foliated mass of interlocking calcite crystals known as marble.

    • Properties of marble:

    • Since it is composed entirely of calcite, it possesses similar characteristics as the mineral.

    • Exhibits effervescence when reacted with acids, a significant distinguishing feature.

  • Sedimentary bituminous coal is primarily composed of highly altered plant matter, predominantly carbon.

    • Upon metamorphism, the carbon content becomes further concentrated, resulting in a non-foliated mass known as anthracite coal.

    • Distinctions of anthracite coal:

    • Can be identified by its shiny, almost obsidian-like luster.

    • Exhibits a brittle nature, contrasting with the more porous structure of bituminous coal.

    • Although all types of coal are considered unclean in environmental terms, anthracite yields more energy with fewer volatile gases when burned, making it a preferred choice for energy generation.

Metamorphic Rock Identification Key

Distinctive Properties

  • The key factors in distinguishing various metamorphic rocks include:

    • Texture: Refers to the physical appearance and feel of the rock.

    • Grain Size: Indicates the size of the mineral grains that comprise the rock.

Rock Classification

  • Common metamorphic rock classifications include:

    • Quartzite: Derived from sandstone (parent rock).

    • Marble: Derived from limestone (parent rock).

    • Anthracite coal: Derived from bituminous coal (parent rock).