IGNEOUS ROCK SPECIMEN

Rocks are simply defined as an aggregate of minerals. There three classifications Igneous Rocks formed  from cooled lava and magma associated with volcanic activity. Sedimentary Rocks formed from compacting sediments (pebbles, sand and clay) often below sea level. Metamorphic Rocks forms from preexisting rocks that get buried and remain in a solid state while immersed at various levels of heat and pressure.   

Igneous Rocks

It is essentially a silicate melt and may contain, as well as silicon and oxygen, other elements, particularly aluminum, iron, calcium, sodium, potassium and magnesium. These combine, as the magma or lava crystallizes, to form silicate minerals, which in combination make up igneous rocks.

Igneous Rocks: Phaneritic “visible crystals” from cooling magmas

Rock name: Red Granite.
Rock type: Igneous “born of fire”.
Composition: Felsic (70% + silica).
Texture: Phaneritic.
Origin: Plutonic (magma).
Sources: Granite composes the core of continents.
Mineral content: Orthoclase (red), Quartz (gray/clear), and Biotite Mica (black).

Rock name: Gabbro.
Rock type: Igneous “born of fire”.
Composition: Mafic/Basic (less than 50% silica).
Texture: Phaneritic.
Origin: Plutonic (magma).
Mineral content: Labradorite (gray/shiny), Augite (black), and sometimes Olivine (green).

Igneous Rocks: Porphyry from two “stage cooling” with phenocryst

Rock name: Diorite Porphyry.
Rock type: Igneous “born of fire”.
Composition: Intermediate (50-70% silica).
Texture: Porphyry.
Origin: Two-stage cooling (magma and lava).
Mineral content: Albite (white), Diorite (gray/clear), Hornblende (black), and Biotite Mica (black).

Rock name: “Blue Quartz” Rhyolite Porphyry (Rare Llanite).
Rock type: Igneous “born of fire”.
Composition: Felsic (70% + silica).
Texture: Porphyry.
Origin: Two-stage cooling (magma and lava).
Source: Nine miles north of Lano, Texas

Rock name: Gabbro Porphyry.
Rock type: Igneous “born of fire”.
Composition: Mafic-Basic (less than 50% silica).
Texture: Porphyry.
Origin: Two-stage colling (magma and lava).

Igneous Rocks: Aphanitic “without visible crystals” from cooling lavas

Rock name: Andesite.
Rock type: Igneous “born of fire”.
Composition: Intermediate (50 to 70% silica).
Texture: Aphanitic.
Origin: Lava flow.
Source: Continental arch and Island arch volcanoes.

Rock name: Basalt with Olivine Xenolith.
Rock type: Igneous “born of fire”.
Composition: Mafic/Basic (less than 50% silica).
Texture: Aphanitic.
Origin: Lava flow.
Source: Ocean crust, island chains, and other volcanoes.

Igneous Rocks: Vesicular from gaseous cooling

Rock name: Scoria.
Rock type: Igneous “born of fire”.
Composition: Intermediate to Mafic (50 to 100% silica).
Texture: Vesicular.
Origin: Gaseous lava.

Rock name: Vesicular Rhyolite (secondary Calcite fill).
Rock type: Igneous “born of fire”.
Composition: Felsic (70% + silica).
Texture: Aphanitic to Vesicular.
Origin: Lava flow.
Source: Continental volcanoes and Calderas.

Rock name: Vesicular Basalt.
Rock type: Igneous “born of fire”.
Composition: Mafic/Basic (less than 50% silica).
Texture: Aphanitic.
Origin: Lava flow.
Source: Ocean crust, island chains, and other volcanoes.

Igneous Rocks: Glassy from rapid cooling

Rock name: Red Obsidian.
Rock type: Igneous “born of fire”.
Composition: Felsic, Intermediate, to Mafic/Basic (100% silica).
Texture: Glassy.
Origin: Lava flow.

Igneous Rocks: Pyroclastic

Rock name: Ignimbrite.
Rock type: Igneous “born of fire”.
Composition: Felsic, Intermediate, to Mafic/Basic.
Texture: Pyroclastic.
Origin: Lava flow.

Igneous Rocks: Pegmatites

Rock name: Feldspar Pegmatite.
Rock type: Igneous “born of fire”.
Composition: Felsic (70% + silica).
Texture: Phaneritic.
Origin: Plutonic (magma).
Sources: Granite composes the core of continents.
Mineral content: Orthoclase (pink), Quartz (gray/clear), Muscovite Mica (gray), and Hornblende (black).

Igneous Rocks: Ultra Mafic origins

Rock name: Basalt with Serpentine veins.
Rock type: Igneous “born of fire”.
Composition: Ultra Mafic/Basic (less than 35% silica).
Texture: Aphanitic.
Origin: Lava flow.
Source: Mafic volcanoes

Data: Pellant, Chris. Smithsonian Handbooks. Rocks and Minerals: The clearest recognition guide available. A Dorling Kindersley Book.