The document discusses the pyroxene group of minerals. Pyroxenes have a single chain crystal structure and are ionosilicates containing elements like calcium, sodium, magnesium, iron, and aluminum. They can be orthorhombic or monoclinic in crystal form. The general chemical formula of pyroxenes is (W,X,Y)2Z2O6, where W, X, Y, and Z can be elements like calcium, magnesium, iron, aluminum, sodium, lithium, silicon, and more. Some common pyroxenes mentioned include enstatite, hypersthene, diopside, hedenbergite, augite, and pigeonite.

1. Pyroxene group.

2. Introduction Pyroxene group includes both monoclinic and orthorhombic minerals. Minerals belonging to this group are ionosilicates having single chain structures. These are the silicates of Ca, Na, Mg, Fe and Al. The crystals are short prismatic with interfacial angles of about 87 º and 93 º.

3. The chemical composition of the pyroxenes can be expressed by the general formula (W,X,Y) 2 Z 2 O 6 in which W, X, Y ,Z indicate elements having similar ionic radii and capable of replacing each other in the structure. In pyroxenes these elements may be : W= Ca, Na X= Mg, Fe 2+ , Mn 2+ , Li Y= Al, Fe 3+ , Ti Z= Si, Al.

4. Manganese is generally present in minor amounts except in the rare pyroxene Johannsenite, Ca Mn Si 2 O 6. Lithium occurs as a major constituent in spodumene, Li Al Si 2 O 6 ORHORHOMBIC Pyroxenes Enstatite- Orthoferrosilite Enstatite- Mg SiO 3 Hypersthene- (Mg, Fe) SiO 3

5. Monoclinic pyroxenes Diopside- Hedenbergite- Johannsenite Ca (Mg, Fe, Mn) Si 2 O 6 Aegirine – Na Fe Si 2 O 6 Jadeite – Na Al Si 2 O 6 Spodumene- Li Al Si 2 O 6 Johannsenite- Ca Mn Si 2 O 6.

6. Augite – intermediate between diopside and hedenbergite with some Al. Pigeonite- intermediate between clinoenstatite and Augite.