APOPHILLITE on BRUCITE, Avebury Mine Zeehan Dundas Tasmania (small cabinet)

Apophyllite designates a specific group of phyllosilicates, which are a category of minerals. Initially, this term referred to a single mineral but was redefined in 1978 to encompass a class of minerals with similar chemical compositions that form a solid solution series, including fluorapophyllite-(K), fluorapophyllite-(Na), and hydroxyapophyllite-(K). The term apophyllite is derived from the Greek word apophyllízo (ἀποφυλλίζω), meaning 'it flakes off,' highlighting the tendency of these minerals to disintegrate upon heating due to water loss. Exfoliation can also occur through acid treatment or simple abrasion. These minerals are commonly found as secondary formations within vesicles of basalt or other volcanic rocks.

Brucite is a mineral composed of magnesium hydroxide, represented by the chemical formula Mg(OH)2. It commonly forms as a result of the alteration of periclase in marble and appears as a low-temperature hydrothermal vein mineral within metamorphosed limestones and chlorite schists. Additionally, brucite is produced during the serpentinization process of dunites. This mineral is frequently found alongside other minerals such as serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc, and chrysotile.