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An interlocking mass of large quartz crystals in which the crystals have grown together (technically termed a 'quartz mass'). The quartz mass in these samples dominates the rock they are embedded in.
Quartz is a hard, durable mineral with a crystalline structure. Angular with some visible flat facets. It has many aesthetic and practical uses, e.g. for jewellery, electronics and glassmaking.
The flat, angular faces make specimens especially suitable for scratch tests to determine hardness.
Mineral: Formed from silica-rich solutions crystallising in cavities and veins.
Source rock and location: Tasman granite.
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Note: Images are examples of specimens only. Sizes, colours and shapes will vary.
More detail
Structure
Quartz has a crystalline structure with a hexagonal crystal system. It is composed of silicon dioxide (SiO₂) arranged in a continuous framework of tetrahedra. Frequently forms chunky clusters of crystals in granite.
Type
Silicate mineral.
Physical properties of quartz
Colour: Highly variable. These samples range from clear, to white, to brownish (smoky quartz) depending on trace impurities and inclusions.
Lustre: Has a vitreous (glassy) lustre, with a greasy sheen at fracture surfaces.
Hardness: A very hard mineral, ranking 7 on the Mohs scale of mineral hardness (can scratch glass and most other common minerals).
Density: Approximately 2.65 grams per cubic centimetre.
Fracture: Exhibits a conchoidal fracture, breaking with smooth, curved surfaces resembling the interior of a seashell; lacks cleavage.
General properties of quartz
Composition: Consists of silicon dioxide (SiO₂), an oxide mineral in the silicate group. Pure quartz is chemically simple, but trace elements (iron, titanium, aluminium, lithium) create colour varieties.
Crystalline Structure: Forms hexagonal prismatic crystals with horizontally striated faces. Large, well-formed crystals are not common in New Zealand but are mainly found in cavities of igneous rocks in Canterbury and Coromandel.
Durability: Highly durable and resistant to chemical weathering, making it one of the most stable and abundant minerals on Earth.
Heat Resistance: Exhibits excellent heat resistance with a melting point of approximately 1750°C, remaining stable at high temperatures.
Piezoelectricity: Quartz is piezoelectric—it produces an electrical potential difference when subjected to mechanical pressure. This property is exploited in electronics, watches, and oscillators.
Low Porosity: Has very low porosity and water absorption, making it resistant to staining and moisture damage.
Uses of quartz in New Zealand and worldwide
Electronics and Technology: Quartz's piezoelectric properties make it indispensable in electronic information, semiconductors, optical light sources, photovoltaic energy, and aerospace applications. Used in watches, radios, computers, and sensors.
Glassmaking: A primary raw material for manufacturing glass, ceramics, and refractory materials due to its high silica content and heat resistance.
Jewellery and Ornamental Stone: Coloured varieties (amethyst, citrine, rose quartz, smoky quartz).
Metallurgical Industry: Acts as a fluxing agent in smelting processes and as a source of silica for metallurgical purposes.
Industrial Applications: Used in casting, ceramics, chemicals, plastics, rubber, and as a filler or abrasive in various manufacturing processes.
Lapidary and Collecting: Popular among rockhounds for specimen collection.
Geological Studies: Studied by geologists to understand igneous, metamorphic, and sedimentary processes, hydrothermal systems, and the geological history of Earth's crust.