Properties and uses of granite, phyllite, limestone

Granite (igneous, intrusive)

• Physical properties: coarse-grained, hard, massive; colour pink, grey or white with quartz, feldspar and mica; specific gravity 2.6-2.8; vitreous lustre.
• Engineering properties: compressive strength 100-250 MPa; porosity less than 1%; low water absorption; very durable; takes a good polish; may have joints and sheet jointing; feldspar weathers to clay.
• Uses: foundations for dams and bridges, building and monument stone, paving blocks, curbstones, aggregate, railway ballast, decorative slabs.

Phyllite (metamorphic, foliated)

• Physical properties: fine-grained, grey, green or black; silky sheen from fine mica; wavy foliation; hardness 3-4; specific gravity 2.7-2.9.
• Engineering properties: compressive strength low to moderate (20-60 MPa), strongly anisotropic; splits along foliation; weathers easily; weak in slopes and tunnels, and often prone to landslides in the Lesser Himalaya (Nepal).
• Uses: limited; roofing and flooring slabs where thick and hard; fill or road sub-base; generally unsuitable as aggregate or for heavy foundations.

Limestone (sedimentary, chemical/organic)

• Physical properties: fine- to coarse-grained, white, grey or yellowish; hardness 3; effervesces with dilute HCl; specific gravity 2.5-2.8.
• Engineering properties: compressive strength 30-150 MPa; soluble in acidic water, so it forms caves and cavities (karst), leading to leakage at reservoirs and settlement of foundations.
• Uses: raw material for cement and lime, aggregate, building stone, flux in metallurgy, flooring, road metal.