LOMONOSOV MOSCOW STATE UNIVERSITY FACULTY OF GEOLOGY «ROCK-FORMING MINERALS OF OLIVINE GROUP» A.B. Shefel
GOALS AND OBJECTIVES Goal: Review of modern literature in order to summarize information about minerals of olivine group Specific questions: Abundance of minerals of olivine group in different kind of rocks Structure and chemical composition of olivines What petrological information may be obtained using olivine
ROCKS CLASSIFICATION IGNEOUS INTRUSIVE EFFUSIVE ROCKS METAMORPHIC SEDIMENTARY
CLASSIFICATION OF MINERALS MINERALS OF MAGMATIC ORIGIN ROCK- FORMING SECONDARY ACCESSORY More 5% Less 5% Quota of percent
MINERALS OF OLIVINE GROUP The most common minerals group isomorphous series: forsterite Mg 2 (SiO 4 ) fayalite Fe 2 (SiO 4 ). This is tetrahedral orthosilicates. http://tikalon.com/blog/2013/olivine_ UK.gif The most common shaped crystals of olivine. Left is a forsterite, right is a fayalite. (Betekhtin., 1951) Group minerals olivine have the following properties: Luster vitreous, greasy. Streak white. Hardness 6,5-7. Cleavage average or imperfect. The fracture is often shelly.
STRUCTURE General formula: А 2 TO 4. A divalent cations (Mg, Fe, Mn, Ni, Zn, Co, Ca, Pb). O T A T three - and tetravalent cations (Si, Al, Ti). The crystal lattice is constructed of individual blocks (А and Б). Tetrahedrons of SiO 4 are directed up and down. Small circles is magnesium ions. Betekhtin, 1951
Ionic radius (nm) FACTORS CONTROLLING MINOR ELEMENT CONTENTS Distribution coefficient and element concentration in melt K D = Х min /Х melt K D = f (T, P)
OLIVINE GROUP MINERALS Forsterite Mg 2 SiO 4 Hortonolite (Mg,Fe) 2 SiO 4 Fayalite Fe 2 SiO 4 Knebelite (Fe,Mn) 2 SiO 4 Tephroite Mn 2 SiO 4 Picrotephroite (Mn,Mg) 2 SiO 4 Chemical composition of main minerals of olivine group. (Betekhtin, 1951)
MINERALS OF GROUP OLIVINE Monticellite CaMgSiO 4 Kirschsteinite CaFeSiO 4 Glaucochroite CaMnSiO 4 Calcio-Olivine Ca 2 SiO 4 Larsenite PbZnSiO 4 Ca-Larsenite PbCaSiO 4 The composition of minerals olivine group in the system Ca-Fe-Mg http://www4.nau.edu/meteorite/meteorite/book-glossaryo.html
ABUNDANCE OF OLIVINE IN MAGMATIC ROCKS Rock group SiO 2 content Examples Ultrabasic 30-45% dunite, olivinite, peridotite, pyroxenite, kimberlite Basic 45-53% gabbro, basalt, labradorite Intermediate 53-65% diorite, andesite, trachyte 65-78% granite, rhyolite
REACTIONS WITH OLIVINE Serpentinization (hydrothermal alteration of olivine) occurs at temperatures below 400 о С Typical weathering of olivine Olivine => serpentine, talc Olivine => serpentine, asbestos, talc, chlorite, magnetite, hematite, limonite In SiO 2 saturated melts orthopyroxene (enstatite) forms instead of olivine: (Mg,Fe) 2 SiO 4 + SiO 2 => (Mg,Fe) 2 Si 2 O 6
OLIVINE GROUP FORMULAS Most common isomorphic components Chemical formula (Mg,Fe,Mn) 2 [SiO 4 ] (Fe,Mg,Mn) 2 [SiO 4 ] (Mn,Fe,Mg) 2 [SiO 4 ] Mineral forsterite fayalite tephroite Some empirical chemical formulas of olivines Chemical formula (Mg 1, 34 Fe 2+ 0, 56 Ca 0, 06 Mn 0,04 ) [SiO 4 ] (Fe 2+ 1.48Mg 0.32 Mn 0.17 Fe 3+ 0.03) [(Si 0.97 Al 0.03 )O 4 ] (Mn 1, 25 Fe 2+ 0, 65 Mg 0,06 Ca 0, 02 ) [SiO 4 ] Mineral forsterite fayalite tephroite The composition of olivine often presented as #Mg=MgO/(MgO+FeO)
OLIVINE IS A VALUBALE SOURCE OF PETROLOGICAL INFORMATION Subduction zone. The heavier oceanic crust sinks under the continental crust. Peridotite xenolith in basalt Tokskoe ore deposit. ~15х8 cm. Photo: А.А. Evseev. http://geo.web.ru/druza/12amu_0.htm
OLIVINE CRYSTALLISATION Olivine settling in magmatic reservoir The heavier olivine in the melt falls to the bottom of gabbroid camera. A.L. Perchuk: http://www.geol.msu.ru/deps/petro/le ctions/petrol/petrolect2.pdf
OLIVINE IN BASALTS http://faculty.chemeketa.edu/afrank1/rocks/igneous/ve sbasalt.htm http://rockhounds.ning.com/photo/pict0004-san-carlos-az http://museumvictoria.com.au/pages/19498/mi00000 6-e12269-basalt.jpg http://www.kutahyacimento.com/tr/kutahya-cimentobazalt-madenciligi
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