Jasper is a variety of chert, a sedimentary rock composed of very finely-crystalline quartz with the red colouration coming from hematite (Fe2O3). Rounded by physical abrasion during river and/or wave transport. Sedimentary: Formed by moderate pressure and heat. Size: Hand specimen. Localities: Coromandel Peninsula, Canterbury, Southland and the eastern North Island. Images are examples of specimens only. Sizes and shapes may vary. More detail Structure Jasper is made of extremely small quartz crystals that are too fine to see individually. It is usually opaque, meaning that light does not pass through it, and may have spots, bands, swirls, cracks or brecciated patterns. Type Silica-rich rock – a fine-grained, opaque variety of chalcedony, which is part of the quartz family. Physical properties Colour: Common colours include red, brown, yellow, cream, green, grey and black. Many specimens have several colours together, often in attractive bands or patterns. Lustre: Usually dull or waxy when it is freshly broken. When polished, jasper can have a smooth, attractive sheen. Hardness: A fairly hard and durable rock, generally around 6.5–7 on the Mohs hardness scale. Density: Moderately heavy, typically around 2.5–2.9 g/cm³. Fracture: Usually breaks with a curved or uneven surface. Freshly broken edges can be quite sharp. General properties of jasper Composition: Mostly silica, with small amounts of minerals such as iron oxides, clay and other inclusions. These extra materials give jasper its wide variety of colours and patterns. Texture: Fine-grained, smooth and generally solid. Some specimens show bands, spots, swirls, small cavities or a brecciated appearance. Durability: Hard and reasonably tough, so it stands up well to handling and everyday wear. It can be scratched by materials that are harder than quartz. Polish: Jasper takes a fine polish, which brings out its colours, patterns and natural sheen. This is one of the main reasons it is popular for lapidary work and ornaments. Water Resistance: Dense jasper absorbs little water and is suitable for many indoor and outdoor decorative uses. Cracked, porous or weathered pieces may be less resistant. Uses of jasper in New Zealand and worldwide Jewellery: Cut and polished into cabochons, beads, pendants, earrings, bracelets and rings. Its unusual patterns mean that each piece is often distinctive. Decorative Objects: Used for bookends, paperweights, polished slices, bowls, vases, small carvings and display pieces. Jasper has been used for ornamental objects for thousands of years. Landscaping: Larger pieces can be used in rockeries, gardens, water features and other decorative settings, especially where a colourful natural stone is wanted. Inlay and Mosaics: Thin slices and small pieces are used in decorative inlay, mosaics, jewellery boxes, furniture and other craftwork. Carvings and Sculptures: Its fine texture and ability to take a good polish make it suitable for small sculptures, figurines, seals and ornamental carvings. Historical Tools: Dense jasper was used in the past for cutting tools, scraping tools, drills and engraved seals because it is hard and breaks to form sharp edges. Collector’s Specimens: Jasper is widely collected for its unusual colours, patterns and local geological character. Polished slices are particularly useful for showing the internal markings of the rock. Geological Interest: Jasper is studied as a silica-rich rock and for the clues its colours and patterns provide about the volcanic and sedimentary environments in which it formed.
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