0 TRAINING ON SURFACE EXPLORATION STUDIES FOR GEOTHERMAL RESOURCES AND DEVELOPMENT OF CONCEPTUAL MODELS UNDER THE AUSPICES OF INTERIM PROJECT COORDINATION UNIT OF THE AFRICA GEOTHERMAL CENTER OF EXCELLENCE Rock types and minerology (Igneous/Sedimentary /Metamorphic) with emphasis Igneous petrology/volcanology Dr. Tobias Björn Weisenberger, Iceland GeoSurvey
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TRAINING ON SURFACE EXPLORATION STUDIES FOR GEOTHERMAL RESOURCES AND
DEVELOPMENT OF CONCEPTUAL MODELS
UNDER THE AUSPICES OF INTERIM PROJECT COORDINATION UNIT OF THE AFRICA
Table 25-1. Definitive Mineral Assemblages of Metamorphic Facies
Mineral assemblages in mafic rocks of the facies of contact meta-
morphism do not differ substantially from that of the corresponding
regional facies at higher pressure.
Low Temperature Metamorphic rocks
Winter (2010) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Igneous rocks
Igneous Rocks - classification
Textures:
Aphanitic: crystals too small to see by eye
Phaneritic: can see the constituent minerals
Fine grained- < 1 mm diameter
Medium grained- 1-5 mm diameter
Coarse grained- 5-50 mm diameter
Very coarse grained- > 50 mm
diameter
Porphyritic: bimodal grain size distribution
Glassy: no crystals formed
Idealized rates of crystal nucleation and growth as a function of temperature below the melting point. Slow cooling results in only minor undercooling (Ta), so that rapid growth and slow nucleation produce fewer coarse-grained crystals. Rapid cooling permits more undercooling (Tb), so that slower growth and rapid nucleation produce many fine-grained crystals. Very rapid cooling involves little if any nucleation or growth (Tc) producing a glass.
Winter (2010) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Intrusive rocks
Porphyry
Pyroclasts
Extrusive rocks
Volcanic ash Bomb PumiceExtrusive pyroclasts form in violent eruptions from lavain the air.
Mafic Felsic
Basalt RhyoliteExtrusive igneous rocks cool rapidly and are fine-grained.