Basalt rock

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Basalt is a fine-grained, hard, dense rock. The most common rock on the Earth, Moon and Mars and it has erupted from volcanoes scattered throughout New Zealand.

Igneous: Rock formed from lava flows (therefore technically a 'volcanic igneous' rock).

Source location: Canterbury.

Sizes: Choose from dropdown menu either Shelf specimen (300–800g), or Hand specimen (less than 300g)

Note: Images are examples of specimens only. Sizes and shapes will vary.

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Basalt is a fine-grained igneous rock with a dense and homogeneous structure. It is typically composed of minerals such as pyroxene, plagioclase feldspar, and olivine.


Volcanic igneous.

Physical Properties of basalt

  • Colour: Typically dark grey or black in colour.
  • Lustre: Dull to glassy lustre, depending on its texture and mineral composition.
  • Hardness: A relatively hard rock, ranging from 5 to 6 on the Mohs scale.
  • Density: Ranges from 2.8 to 3.0 grams per cubic centimetre.
  • Fracture: Exhibits a conchoidal fracture, meaning it breaks with smooth, curved surfaces resembling the interior of a seashell.

General Properties of basalt

  • Fine-Grained Texture: Has a fine-grained texture due to its rapid cooling from lava or magma, resulting in small mineral crystals.
  • Interlocking Structure: Its minerals form an interlocking structure, contributing to its strength and durability.
  • Weather Resistance: Highly resistant to weathering, erosion, and chemical attack, making it suitable for outdoor applications.
  • Heat Resistance: Has excellent heat resistance and can withstand high temperatures without significant deformation or damage.
  • Low Porosity: Relatively low in porosity, making it less susceptible to water absorption and freeze-thaw damage.

Uses of basalt in New Zealand and worldwide

  • Early Māori: Basalt (karā) was used to make stone clubs (patu ōnewa).
  • Construction: Widely used as a construction material, including for building facades, walls, and road construction.
  • Paving: Its durability and resistance to weathering make it suitable for paving stones, footpaths, and driveways.
  • Landscaping: Used in landscaping projects for retaining walls, decorative features, and pathways due to its natural beauty and durability.
  • Aggregate: Crushed basalt is used as aggregate in concrete, asphalt, and road construction.
  • Railway Ballast: Utilised as railway ballast, providing stability and drainage to railway tracks.
  • Dimension Stone: Can be cut and polished into slabs for architectural purposes, including countertops, tiles, and monuments.
  • Geological Studies: Studied by geologists to understand volcanic processes, lava flows, and the history of Earth's crust.