fabric

In mining geology, fabric describes the physical arrangement, size, and orientation of mineral crystals within a rock body. It is the three-dimensional pattern you observe when you examine a rock specimen, especially under magnification or in thin section under a microscope. Fabric reveals how the rock formed, how it has been deformed, and whether it has economic value as an ore deposit.

The primary components of fabric are grain size, grain shape, and the preferred orientation of grains relative to each other. A granite may have a coarse equigranular fabric, where feldspars, quartz, and mica crystals are roughly the same size and randomly oriented. A metamorphic schist, by contrast, shows strong foliation, a fabric in which plate minerals like mica are aligned parallel to each other, giving the rock a pronounced layered appearance. Igneous rocks near the contact with country rock often develop a fine-grained porphyritic fabric, with large crystals (phenocrysts) set in a much finer-grained matrix.

Fabric and ore deposit character

Miners and geologists use fabric to infer whether an ore body has been subject to deformation, hydrothermal alteration, or weathering. A sulfide ore with a massive fabric (densely interlocked grains with no preferred orientation) behaves differently during crushing and milling than one with a disseminated fabric, where ore minerals are scattered through a waste-rock host. Cataclastic fabrics, created by mechanical fracturing and grain size reduction under stress, may indicate proximity to a fault or fold and can affect metallurgical recovery rates. Oxidized or leached zones often show a brecciated fabric marked by angular fragments cemented together, signaling chemical breakdown.

Fabric terminology varies slightly between mineral exploration, metamorphic geology, and mining engineering. Geotechnical engineers use fabric to assess rock mass competence and stability; a well-interlocked igneous fabric will stand at steeper angles than a platy metamorphic one. Metallurgists test fabric patterns in ore samples to predict liberation, how cleanly valuable minerals will separate from waste, during concentration and smelting.

The term originated in petrography, the microscopic study of rocks, and remains essential to core logging, resource estimation, and open-pit or underground mine design. A single ore deposit may contain multiple fabrics in different zones; understanding this spatial variation is critical to grade control and processing decisions.