Igneous Rocks -- II
Intermediate Rocks
Acidic Rocks
Classifications: minerals & chemical compositions
Intermediate Rocks
Texture Alkali feldspar < 1/3
Alkali feldspar >1/3 < 2/3
Alkali feldspar >2/3
Feldspathoidal
Volcanic rocks
Andesite Trachyandesite (latite)
Trachyte Phonolite
Plutonic rocks
Diorite Monzonite Syenite Feldspathoidal syenite
Diorite
• Definition: is intrusive, holocryatalline, phaneritic, containing:
• Plagioclase (oligoclase or andesine)-----55~70%
• Mafic (commomly hornblende or biotite)----- 40~25%
Diorite:Plag+ Mafic ( Hb, Cpx, Bi)
Trachytoid Diorite
Andesite
• Definition: is volcanic and hypabyssal intrusive, holocryatalline or hypocrystalline, with matrix aphanetic, containing:
• Plagioclase (oligoclase or andesine)-----55~70%
• Mafic (commomly hornblende or biotite)----- 40~25%
Andesite:
Plag+Mafic (Cpx, Hb, Bi)
Porphyritic Andesite
High-Mg andesite:
Plag+Opx+Ol
Tonolite (quartz andesite)
• Definition: is intrusive, plutonic and hypabyssal, holocryatalline, phaneritic, containing:
• Sodic plagioclase (oligoclase or andesine)-----50~80%
• Quartz ---- 35~10%
• Mafic (biotite and hornblende)----- 35~10%
Tonalite:Plag+Mafic (Bi, Hb) +quartz (< 10%)
Dacite (quartz andesite)
• Definition: is volcanic and hypabyssal intrusive, holocryatalline or hypocrystalline, with matrix aphanetic, containing:
• Sodic plagioclase (oligoclase or andesine)-----50~80%
• Quartz ---- 35~10%
• Mafic (biotite and hornblende)----- 35~10%
Dacite:Plag+Mafic (Bi, Hb) +quartz (< 10%)
Monzonite
• Definition: is intrusive, Plutonic or hypabyssal, holocryatalline, phaneritic, containing:
• Mafic (hornblende, biotite, augite)----- 15~60%
• Sodic Plagioclase (oligoclase or andesine)-----50~30%
• Potash feldspar (orthoclase) ----- 45~25%
Monzonite:Plag+K-feldspar +Mafic (Bi, Hb, Aug)
Latite
• Definition: is volcanic and hypabyssal intrusive, holocryatalline or hypocrystalline, with matrix aphanetic, containing:
• Mafic (hornblende, biotite, augite)----- 15~60%
• Sodic Plagioclase (oligoclase or andesine)-----50~30%
• Potash feldspar (orthoclase) ----- 45~25%
Syenite
• Definition: is intrusive, Plutonic or hypabyssal, holocryatalline, phaneritic, containing:
• Alkali feldspar (orthoclase) ----- 30~80%
• Sodic Plagioclase (oligoclase or andesine)-----5~25%
• Mafic (hornblende, biotite, augite)----- 40~10%
Syenite:
K-feldspar+ Plag +Mafic (Bi, Hb, Px)
Trachyte
• Definition: is volcanic and hypabyssal intrusive, holocryatalline or hypocrystalline, with matrix aphanetic, containing:
• Alkali feldspar (orthoclase) ----- 45~80%
• Sodic Plagioclase (oligoclase or andesine)-----5~25%
• Mafic (hornblende, biotite, augite)----- 30~10%
Trachyte:K-feldspar+ Plag +Mafic (Bi, Hb, Px)
Acidic rocks or Silicic Rocks
Granite
Rhyolite
Granodiorite
Quartz latite
Granite
• Definition: is plutonic, intrusive, and hypabyssal, holocryatalline, phaneritic, containing:
• Quartz ----- 10~40%• Potash feldspar ----- 30~60% • Sodic plagioclase (excluding perthite)-----
0~35%• Mafic (biotite, hornblende)----- 40~25%
Calc-alkali granite
• Perthitic orthoclase or microcline
• Oligoclase or rarely andesine
• Hornblende• Diopside or augite
Alkali granite
• Strongly perthite orthoclase or microcline, anorthoclase
• Albite or sodic oligoclase
• Iron-rich biotite• Hastingsite, arfvedsonite,
riebeckite• Aegirine-augite, rarely
hedbergite
Granite
Granite
Granite:
Or + Qz + Mica (Bi, Mus)
Microcline
Perthite
Alkali granite:Or + Qz + Alkali Hb
Rhyolite
• Definition: is volcanic and hypabyssal, holocryatalline or hypocrystalline, with matrix aphanetic, containing:
• Quartz ----- 10~40%• Potash feldspar ----- 30~60% • Sodic plagioclase (excluding perthite)-----
0~35%• Mafic (biotite, hornblende)----- 40~25%
Rhyolite
Rhyolite
Obsidian
Rhyolite:Or + Qz
Rhyolite:Or + Qz
Pumice
Granodiorite
• Definition: is plutonic and intrusive, holocryatalline, phaneritic, containing:
• Potash feldspar ----- 20~40%
• Sodic plagioclase-----25~45%
• Quartz ----- 35~10%
• Mafic (biotite, hornblende)----- 30~10%
Granodiorite:Or + Plag + Qz + Mafic (Bi, Hb)
Granodiorite:Or + Plag + Qz + Mafic (Bi, Hb)
Quartz latite
• Definition: is volcanic and hypabyssal, holocryatalline or vitrous, with matrix aphanetic, containing:
• Potash feldspar ----- 20~30%
• Sodic plagioclase-----30~50%
• Quartz ----- 35~10%
• Mafic (biotite, hornblende)----- 20~10%
Ultrabasic and basic rocks
Classifications: minerals & chemical compositions
Definition
• Peridotite is holocrystalline, phaneritic, plutonic rocks; containing
• Mafic (Ol, Px, Hb) --------- 85-95%
• Ores (magnetite, ilmenite, chromite)---10-3%
• Calcic plagioclase ------< 5%
Classification
• Peridotite ---- group name• Ol ------- Dunite• Ol + OPX (En or Hy) ----Harzburgite• Ol + CPX (aug) -------- Wehrite• Ol + OPX + CPX ---- Lherzolite• Ol + Hb -------- Cortlandtite• Px (CPX + OPX) ----- Pyroxenite• Hb ---------- Hornblendite• Kimberlite --- mica peridotite
Dunite—olivine + chromium-rich spinel
Harbuzite—Olivine + OPX
Wehrite—Olivine + CPX
Lherzolite—Olivine + OPX + CPX
Garnet peridotite
Pyroxenite--- CPX + OPX
Hornblendite--- Hb
Kimberlite --- mica peridotite
Fine-grained ultramafic rocks
• Komatiite
• ankaramite --- Diopside augite
• Limburgite --- Augite
• Katungite --- melilite-rich Ol leucitite
• Ugandite --- melanocratic Ol leucitite
• Melilitite & nephelinitite --- nepheline basalt
• Basanite
Komatiite
Leucitite
Meymechite
Basanite
Ultramafic vs. Ultrabasic
• Mafic mineral: > 70%• Ultramafic ultrabasic
• SiO2 < 45 wt%• Ultrabasic ~ ultramafic• Ex. Carbonatite,
anorthosite
Carbonatite
Basic rocks
• Volcanic rocks:
Tholeiite:
Cpx+Plag
Alkali basalts:
Plag+Cpx+Ol
Picrite: Ol Plag
• Plutonic Rocks
Diabase
Gabbro: Plag + Cpx
Norite: Plag + Opx
Eucrite: Calcic Plag + Opx
Troctolite: Ol +Plag
Anorthosite: Plag Mafic
Gabbro
• Definition: is intrusive, plutonic, holocrystalline, phaneritic rocks.
Containing:
Mafic (aug, Hy, or Ol less commomly Hb) ---25-50%
Plagioclase (labradonite or bytownite) ---- 70-45%
Classifications
• Gabbro --- Aug + Calcic Plag
• Ol-gabbro --- Aug + Ol + Calcic Plag
• Troctolite --- Ol + Calcic Plag
• Norite --- Hy + Calcic Plag
• Anorthosite --- Ol + Calcic Plag
Diabase (dolerite)
• Definition: is intrusive, hypabyssal, normally holocrystalline
Containing
Mafic (aug, Hy, less commomly Ol) ---65-25%
Plagioclase (labradonite or bytownite) ---- 30-70%
Basalts
• Definition: is volcanic and uncommonly hypabyssal intrusive, holocrystalline, hypocrystalline rarely vitrous matrix aphanitic.
Containing
Plagioclase (labradonite) ---- 40-60%
Mafic (aug, Ol) ---55-35%
Tholeiitic basalt:
Cpx Plag ± Ol
Alkali basalt:Plag + Ol Cpx
Lunar low-Ti basalt:Plag + Ol Cpx
Lunar high-Ti basalt:Plag Cpx ± Ol
Picrite basalt: Ol Cpx±Plag
Glassy groundmass
Vesiculated basalt
Gabbro:Plag+Cpx
Alkali gabbro:Plag+Cpx±Ol
Alkali Gabbro:
Plag+Ol+Cpx±K-feldspar or ±Feldspathoid
Basic dike rocksDiabase
Norite:Plag+Opx
Anorthosite:
Plag ± Mafic (< 10%)