Enstatite, pyroxene, MgSiO

Si04 units share two corners to form infinite chains (Figure 1.52(c)). The repeat unit is SiOs . Minerals with this structure are called pyroxenes (e.g., diopside (CaMg(S 103)2) and enstatite (MgSiOs)). The silicate chains lie parallel to one another and are linked together by the cations that lie between them. 

Analysis of lunar rocks returned by Apollo astronauts reveals the presence of three major minerals, which occur in concentrations of more than 10 percent in some rocks an equal number of minor minerals, which occur in concentrations of 1 and 10 percent and a somewhat larger number of minerals that occur in only very small quantities, always less than 1 percent. The chart on pages 223-224 lists these minerals. Many of these minerals occur in more than one form. For example, the various forms of pyroxene differ in what cation is present (iron, magnesium, and/or calcium). Enstatite, one form of pyroxene, has the formula MgSiOs wollastonite is CaSi03 and hedenbergite is CaFeSi206. 

I) that these are called the ordinary chondrites these constitute 35%, 38% and 8%, respectively, i.e. >80% of all falls Obviously, chondrite compositions with elements apportioned by chemical form are not continuous but, rather, quantized. Elsewhere (/) I list major element ratios diagnostic of specific chondritic groups. The total iron in some enstatite (E) chondrites - i.e. those in which the ferromagnesian silicate pyroxene (and the other low-Ca one, olivine) is Fe- and Ca-free MgSiOs - exceeds that in the H group of ordinary chondrites, denoting them as EH chondrites the EL chondrite designation is self-evident. 

Enstatite The Mg-rich pyroxene group endmember mineral with the formula MgSiOs. 

Plate 7 Pyroxene Crystal. 7a 2010 Augite-La Panchita Mine, Mun de La Pe, Oaxaca, Mexico by Rock Currier. 7b 2010 Enstatite-83152 by Rob Lavinsky. 7c 2011 Diopside Aosle by Didier Descouens. Pyroxene is Ca-Mg-Fe silicate ((Ca, Mg, Fe) Si03) and classified as augite (Ca, Mg, Fe) Si20s (Plate 2A), enstatite (MgSiOs) (Plate 2B), diopside (CaMgSi20s, (Plate 2C). It occurs in volcanic rocks (basalt, andesite) and skam-type deposits (see Chap. 1)... 

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