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%)