Jasper

Hardness (Mohs): 6.5-7. Color: Yellow, orange, brown, red, green, black. Luster: Vitreous to greasy. Crystal Structure: Trigonal. Cleavage: None. Specific Gravity: 2.65-2.91.

Jasper generally forms as chemical sedimentary rocks or as hydrothermal deposits in various geological settings. It originates from the precipitation of silica from aqueous solutions, often infilling cavities or replacing existing materials. The distinct banding or patterns often seen in jasper are a result of variations in mineral impurities or depositional conditions. Its age can vary significantly depending on the deposit, ranging from Precambrian to relatively recent.

Jasper is primarily used as an ornamental stone, particularly for cabochons, beads, and carved objects in jewelry. Its varied colors and patterns make it highly desirable for decorative purposes. It's also used in lapidary arts for sculptures and intarsia, and sometimes as a facing stone in construction for decorative accents.

Jasper is a type of chalcedony, which is a microcrystalline variety of quartz. It often forms through the precipitation of silica from hot waters, leading to its characteristic fine-grained texture and vibrant colors due to impurities. The term 'jasper' itself comes from the Greek word 'iaspis', meaning 'spotted stone'. In ancient times, jasper was used for seals and carvings and was believed to have protective and healing properties by various cultures.

In the field, jasper can be identified by its opaque nature and waxy to dull luster. It will scratch glass and is harder than most common rocks. Its distinct colors and patterns, especially reds, yellows, browns, and greens from iron inclusions, are key identifiers. It's commonly found in sedimentary and volcanic regions worldwide, often in association with chert, volcanic rocks, and hot spring deposits. Good localities include parts of the United States (Oregon, Idaho, California), Russia, India, Australia, and Brazil. For collectors, look for specimens with interesting patterns, vibrant colors, or unique forms as these are highly valued.