Mineral Species: Quartz var. Moss Opal 

Chemical Formula: SiO2

Chemical Name: Silicon Dioxide

Mineral Class: Tectosilicate

Mineral Notes: Opal is a variety of Quartz formed from microspheres of SiO2.nH2O, precipitated from silica gel into layers or nodules in veins and cavities of volcanic and sedimentary rocks. The mineral often shows an internal play of colours as light entering the structure is diffracted from the regulalry shaped and spaced spheres. Moss Opal is a variety containg small dendritic inclusions.

Description: A nodule of Moss Opal. The outside is formed from white Quartz whilst the centre has the typical Opal form, which shows a degree of opalescence. Close inspection of the semi-transparent interior shows small dendritic inclusions which gives the mineral its name.

Location: Juniper Ridge Opal Mine, Lake Co., Oregon, USA.