Metamorphic Rock Quiz to Learn Rock Types Easily

Quartzite forms when quartz sandstone is exposed to high heat, causing quartz grains to recrystallize and fuse tightly. This transformation changes the rock's texture into a hard, interlocking mosaic of quartz crystals. The absence of foliation results from uniform mineral composition. Understanding the mineral stability diagram shows quartz remains stable at high temperatures, explaining why sandstone composed mainly of quartz transitions into a very dense and durable metamorphic product.

Slate forms through low grade metamorphism of shale, where clay minerals realign into thin, parallel layers. Under increasing pressure, platy minerals orient perpendicular to the stress direction, creating slaty cleavage. This structural change reduces grain size and increases rock strength. Petrologic thin section analysis reveals fine mineral alignment contributing to its smooth breakage. The process demonstrates the early stages of foliation before more intense metamorphism produces phyllite or schist.

Marble originates when limestone undergoes recrystallization under heat and pressure. Calcite crystals grow larger and interlock, transforming the rock into a denser and more uniform material. Chemical analysis shows the CaCO₃ composition remains the same, but its texture becomes crystalline. This metamorphic process removes fossils and sedimentary structures. Marble’s reaction with dilute acid confirms calcite presence. The new crystal network improves polishability, explaining its widespread use in carving and architecture.

Slate represents the earliest stage of foliated metamorphism. When shale is compressed, clay minerals reorient into a planar fabric. The resulting cleavage allows slate to split smoothly. Microscopic studies show clay and mica minerals forming parallel stacks, reducing porosity and increasing durability. This structural transformation reflects low temperature and pressure conditions before the rock progresses toward phyllite or schist, demonstrating predictable metamorphic pathways observed in pressure temperature diagrams.

Schist contains visible mica crystals that grow during medium grade metamorphism. Micas such as muscovite and biotite enlarge as temperatures rise, creating a shiny, reflective surface. Mineral alignment develops due to directed pressure, enhancing schistosity. Thin section observations show elongated mica grains forming a planar structure. The metamorphic conditions required typically exceed those of slate and phyllite, placing schist in an intermediate stage of the metamorphic sequence.

Hornfels results from thermal metamorphism when surrounding rock is exposed to intense heat from magma. Its fine grained, compact texture forms because minerals recrystallize quickly under high temperature gradients. Petrographic examination reveals equigranular crystals lacking foliation. This structure indicates that heat, not pressure, was the primary metamorphic driver. Hornfels can form from shale, sandstone, or basalt, each displaying different mineral assemblages depending on original chemistry.

Marble’s softness, due to calcite’s low hardness, makes it ideal for sculpture. Under metamorphism, calcite grains grow and form a tight crystalline structure. This uniformity allows for precise carving while maintaining durability. Measurements of Mohs hardness and grain interlocking explain its balance of workability and strength. Its homogenous texture also helps resist fracture planes, giving artists and builders a predictable material for shaping and finishing.

Gneiss develops distinct banding because minerals separate under intense directional pressure. Lighter bands typically contain feldspar and quartz, while darker layers contain biotite or amphibole. This segregation occurs through metamorphic differentiation during high grade conditions. The foliation patterns indicate strong stress fields and prolonged metamorphism. Textural analysis shows gneiss forms deeper in the crust where temperatures and pressures exceed those required for schist, producing coarse layers and visible mineral alignment.

Hornfels forms during contact metamorphism, where country rock is baked by nearby magma. The heat causes recrystallization without significant pressure, producing a hard, fine grained rock. Because temperature gradients vary sharply near intrusions, minerals reorganize into a dense mosaic. The lack of foliation results from uniform heating rather than directional stress. Hornfels is often identified by its toughness and sonic velocity measurements, indicating tightly interlocking minerals.

Gneiss represents the highest grade of common foliated rocks. It forms under extreme temperature and pressure where minerals separate into distinct layers. Feldspar rich domains and dark ferromagnesian layers alternate due to metamorphic banding. Laboratory experiments simulating high grade environments show mineral reorganization driven by diffusion and recrystallization. Gneiss forms from schist or igneous parent rocks like granite, illustrating the upper limit of regional metamorphism before partial melting may occur.