Igneous My Love

+ minerals to memorize

Laccoliths

Mushroom shaped intrusion

Lopolith

Lenticular sunken intrusion, always layered

Stratovolcanoes

Alternating layers of pyroclastic fragments and lava flows

Columnar Joints

• indication of rapid cooling of lava flows, contraction during cooling

• perpendicular to plane of cooling

Key Minerals in Granite / Rhyolite

• biotite

• muscovite

• plagioclase

• k-feldspar

• quartz

Key Minerals for Diorite / Andesite

• Hornblende

• Albite

• Anorthite

Key Minerals for Gabbro / Basalt

• Enstatite + Ferrosilite (opx)

• Diopside + Hedenbergite (cpx)

• Hornblende

• Anorthite

Key Minerals in Peridotite and Komatiite

• Olivine (forsterite + fayalite)

• Opx

• Cpx

Komatiite

• spinifex texture indicating very quick cooling

• long crystals of olivine and pyroxene

• only in Archean and Proterozoic

Biotite

KFe₃ [AlSi₃O₁₀](OH)₂

Muscovite

KAl₂ [AlSi₃O₁₀](OH)₂

Albite

Na[AlSi₃O₈]

Anorthite

Ca[Al₂Si₂O₈]

K-Feldspar

K[AlSi₃O₈]

Hornblende

Ca₂Mg₅ [Si₆Al₂O₂₂](OH)₂

Enstatite

Mg[SiO₃]

Ferrosilite

Fe[SiO₃]

Hedenbergite

FeCa[SiO₃] ₂

Diopside

MgCa[SiO₃] ₂

Forsterite

Mg₂[SiO₄]

Fayalite

Fe₂[SiO₄]

Andalusite, Kyanite, Sillimanite

Al₂SiO₅

Glaucophane

Na-Al Amphibole

Actinolite

Ca-Mg Amphibole

Jadeite

NaAlSi₂O₆

Hydrous Minerals

• all amphiboles (hornblende, actinolite, and glaucophane)

• biotite + muscovite

• talc

• serpentine

• chlorite

• lawsonite

• stauolite

• epidote

Bowen’s Reaction Series: Discontinuous

1. Olivine

2. Pyroxene

3. Amphibole

4. Biotite

5. K-feldspar

6. Muscovite

7. Quartz

Refactory end members

Mg and Ca (Forsterite and Anorthite melt last / crystallize first)

Fusible end members

Fe and Na (Fayalite and Albite melts first / crystallizes last)

Modal Layering

Variation in relative proportion of minerals

Cryptic Layering

• not visible to naked eye

• variation in chemical composition of minerals

Rhythmic Layering

Layers that systematically repeat

Adiabat

P-T path of material which rises quickly and does not exchange heat with surroundings.

Diorite/Andesite Composition

65% Plagioclase

Granite/Rhyolite Composition

30% plagioclase, 30% k-feldspar, 30% quartz, 10% biotite

Gabbro/Basalt Composition

50% pyroxene, 50% anorthite