Zircon

Hardness: 6.5-7 on the Mohs scale. Color: Commonly brown, reddish-brown, yellow, green, or colorless. Luster: Vitreous to resinous. Crystal Structure: Orthorhombic. Typically occurs as rounded pebbles due to alluvial transport. No distinct cleavage; exhibits conchoidal fracture.

Zircon forms in various geological environments, including igneous rocks (especially felsic igneous rocks like granite and syenite), metamorphic rocks, and as detrital grains in sedimentary rocks. It crystallizes from magma as a primary accessory mineral. Its strong resistance to weathering means it can persist through multiple cycles of erosion, transport, and deposition, often ending up as rounded grains in placers. The geological age of the mineral can be billions of years old, making it valuable for radiometric dating.

Zircon is a primary source of zirconium, which is used in ceramics, refractories, and in the nuclear industry. It is also used as a gemstone, particularly the colorless variety (often mistaken for diamond) and the blue variety (which is heat-treated). Due to its high refractive index and excellent dispersion, it has a brilliant sparkle. In its raw form, as shown, it may be collected as a mineral specimen.

Zircon is one of the oldest minerals on Earth, with some zircons found in Australia dating to 4.4 billion years old. Due to its high resistance to weathering and ability to incorporate trace elements, it's often used in geochronology and provenance studies. It's also an important ore of zirconium and hafnium.

In the field, zircon is often found as small, heavy, rounded grains in alluvial deposits (riverbeds, beach sands) due to its resistance to weathering and high specific gravity. Its high hardness can be tested with common materials (it will scratch glass). While crystal forms can be prismatic, weathered specimens like the one pictured are often anhedral and rounded. Common locations include Australia, South Africa, Brazil, and parts of the United States. Identifying specific gravity and hardness, along with its characteristic brown or reddish-brown color in alluvial settings, can help in field identification.