What is granite and how is it used?

Granite is a coarse-grained igneous rock formed from slowly cooled magma, primarily composed of quartz, feldspar and mica minerals that create its characteristic speckled appearance. Architects and designers specify granite for flooring, worktops, external paving, cladding and structural elements due to its proven durability across centuries of use in demanding environments.

Granite consists mainly of quartz (20-60%), alkali feldspar and plagioclase (50-70% combined), with biotite or muscovite mica (5-15%) providing dark flecks against lighter crystals. Its high silica content (70-77% SiO₂) and phaneritic texture—visible interlocking grains—distinguish it from finer-grained igneous rocks or metamorphic stones.

This composition yields hundreds of varieties from global quarries, ranging from pale grey to deep black, pink or green, influenced by feldspar type and trace minerals like iron oxides. Granite differs from marble, which is softer and carbonate-based, and from basalt, which lacks visible crystals due to rapid cooling.

Magma rich in silica and aluminium rises buoyantly through the crust but cools slowly at 5-30 km depth over millions of years, allowing quartz and feldspars to crystallise first into a granular matrix. Micas and accessory minerals fill interstices as temperatures drop, locking the structure before exposure by erosion.

Quarrying uses diamond wires and explosives to extract blocks, which sawmills cut into 2-3 cm slabs using water-cooled gangsaws. Slabs undergo epoxy resin impregnation if needed, calibration for flatness, and finishing—polished, honed, flamed or sandblasted—to suit interior or exterior applications.

Granite achieves Mohs hardness of 6-7, compressive strength of 100-300 MPa and low porosity (0.4-2%), enabling high load-bearing and freeze-thaw resistance. Density (2.6-2.75 g/cm³) provides stability, while chemical inertness resists acids, pollutants and stains better than marble.

Appearance varies by mineral balance: potassium feldspar yields pinks, plagioclase greys, quartz translucency. Finishes alter perception—polish maximises depth and light reflection, texture enhances grip. Thermal conductivity suits underfloor heating; non-combustibility supports fire-rated assemblies.

Kitchen worktops and islands leverage granite’s heat tolerance and robustness for heavy use. Bathroom vanities, shower thresholds and floors benefit from low absorption and cleanability.

Internal flooring graces lobbies, staircases and retail; cladding defines feature walls and plinths. Externally, paving, copings, facades and memorials endure traffic, salt and cycles. Bespoke elements include columns, balustrades and furniture bases.

Granite endures centuries with minimal degradation, as evidenced by ancient obelisks and cathedrals, offering low lifecycle costs. Vast colour palette and unique slab patterns enable creative expression without repetition risks.

Predictable engineering properties simplify structural detailing; low maintenance post-sealing suits commercial hygiene standards. Global supply chains ensure availability, while standard tooling compatibility streamlines fabrication.

High density necessitates structural assessment for cladding or overhangs, with careful handling to avoid edge damage. Polished surfaces slip when wet, requiring textured alternatives in circulation zones.

Sealers degrade over 1-5 years in high-use areas, demanding reapplication; some granites show natural fissures that may propagate under thermal shock. Radioactive trace elements exist but rarely exceed safe limits.

Granite balances marble’s drama with quartzite’s toughness but lacks engineered uniformity.

Material	Hardness (Mohs)	Porosity	Acid Resistance	Cost Range
Granite	6-7	Low	High	Medium
Marble	3-4	Moderate	Low	Medium-High
Quartzite	7	Low	High	Medium-High
Engineered Quartz	7	Very Low	High	Medium

Apply penetrating sealer immediately post-installation, reapplying every 1-3 years per traffic and exposure. Use pH-neutral cleaners and microfibre cloths; ban acids, abrasives or steam on sealed surfaces.

Sweep grit from floors; blot spills instantly. Repolish professionally to correct dullness or etch marks. External granite needs occasional pressure washing below 60 bar.

Engage fabricators during design for slab layout, veining continuity and performance matching to spans or environments. They optimise bookmatching, mitres and fixings for facades, stairs or counters.

Complex curves, large panels or heritage integrations demand workshop expertise for tolerances, movement joints and trade coordination. Early sourcing secures rare varieties and mitigates lead times.