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Sandstone is a sedimentary rock formed from cemented sand-sized grains. It is one of the most common sedimentary rocks found on Earth and is extensively distributed throughout New Zealand, particularly in the North Island.
Sedimentary: Rock formed from the accumulation and cementing together of sand-sized grains.
Source locations: Extensive occurrences throughout New Zealand, especially in Auckland, Taranaki, King Country, Wairarapa, and Southland.
Sizes: Choose from dropdown menu either Shelf specimen (about 300–800g), Hand specimen (about 200–300g) or Small specimen (less than 200g).
Note: Images are examples of specimens only. Sizes and shapes will vary.
More detail
Structure
Sandstone is a sedimentary rock composed mainly of sand-sized silicate grains, such as quartz and feldspar, cemented together by minerals like silica, calcium carbonate, or iron oxide. Its structure can exhibit distinctive sedimentary features like bedding, cross-bedding, and ripple marks.
Type
Clastic sedimentary. (A rock composed of broken pieces of older rocks and deposited as sediments by water or air.)
Physical Properties of sandstone
Colour: Highly variable, ranging from grey, yellow, red, to white, depending on the mineral composition and cement.
Lustre: Generally dull, but can appear more vibrant depending on the presence of minerals.
Hardness: Variable, from soft to hard, depending on the clast and cement composition, typically ranging from 6 to 7 on the Mohs scale for harder varieties.
Density: Ranges from 2.2 to 2.8 grams per cubic centimetre.
Fracture: Can exhibit conchoidal fractures, though not as commonly as in glassy rocks like obsidian.
General Properties of sandstone
Grain size and texture: Sandstone has a grain size of 0.06 to 2 mm, which is visible to the naked eye, and a gritty texture similar to sandpaper.
Porosity and permeability: Highly porous and permeable, making it an excellent reservoir for fluids like water and oil.
Weather resistance: Varies depending on the type of cement; some types are more resistant to weathering than others.
Workability: Easy to work with due to its relatively soft nature compared to other rocks like granite.
Uses of sandstone in New Zealand and worldwide
Construction: Widely used as a building material for facades, walls, and paving due to its durability and aesthetic appeal.
Paving and flooring: Suitable for walkways, patios, and pool surrounds because of its strength and slip-resistant qualities.
Monuments and sculptures: Often used for historic monuments and sculptures due to its ability to be carved into intricate designs.
Gravel and aggregate: Crushed sandstone is used as gravel and aggregate in road construction and concrete production.
Water filtration: Used in water filtration systems due to its porosity.
Grindstones: Coarser varieties are used to make grindstones for sharpening tools and weapons. Early Māori used them for this purpose.
Geological Studies: Important for understanding sedimentary processes and Earth's history.