Jasper

Jasper is an opaque form of Chalcedony, which is a microcrystalline variety of the mineral Quartz. It often contains an abundance of impurities, and therefore some regard it as a rock instead of a mineral. Jasper is usually associated with brown, yellow, or reddish colors, but may be used to describe other opaque colors of Chalcedony such as dark or mottled green and orange. Some forms of Jasper are banded, these banded Jaspers may appear similar to Agate, but unlike Agate they are opaque. 

Geologically the name Jasper has long been used for an opaque to slightly translucent, generally red or brown to variably colored, impure Chalcedony or microcrystalline Chert, usually containing abundant fine inclusions of Hematite, iron hydroxides and other minerals. It is typically associated with banded iron formations.

Color: Brown, yellow, orange, red, green, or blue. Jasper is usually multicolored or banded.

Hardness: 6.5-7 on Mohs scale.