GEO LAB #2

Cleavage

The tendency of a mineral to break along planes of weaker atomic bonding.

Fracture

Random breakage in a mineral where the bonding strength between atoms is equal in all directions.

Lustre

The way a mineral reflects light from its surface.

Streak

Considered more reliable for identification than a mineral's color.

Hardness

A mineral's ability to resist abrasion.

Conchoidal Fracture

A specific type of fracture that is smooth and curved, often seen in quartz and obsidian.

Vitreous Lustre

An appearance best described as glassy.

Fibrous Lustre

Characteristic of minerals with a fibrous structure, like some forms of asbestos.

Earthy Lustre

A mineral lustre described as 'Earthy'.

Streak Color of Hematite

Always leaves a red streak.

Hardness vs. Porcelain Streak Plate

If a mineral is harder than the porcelain streak plate, it will not leave a streak.

Magnetite

The defining diagnostic property of the mineral is its magnetism.

Reaction with HCl

Dropping dilute HCl on a carbonate mineral like calcite will produce effervescence.

Salty Taste Mineral

Halite is known for having a salty taste.

Double Refraction

The ability of calcite to produce a double image when you look through it.

Striations

The tiny parallel lines that seem to be etched onto the cleavage surfaces of plagioclase feldspars.

Labradorescence

The bluish or purplish play of color seen in some Ca-rich plagioclase feldspars.

Phaneritic Texture

Characterized by coarse, visible interlocking crystals.

Cooling History of Phaneritic Rocks

Indicates slow cooling history for an igneous rock.

Aphanitic Texture

Characterized by fine-grained crystals that are too small to see without magnification.

Cooling History of Aphanitic Rocks

Indicates rapid cooling history for an igneous rock.

Porphyritic Texture

Consists of two different crystal sizes.

Phenocrysts

In a porphyritic rock, the larger, early-formed crystals.

Groundmass

In a porphyritic rock, the fine-grained material surrounding the larger crystals.

Cooling History of Porphyritic Rocks

Indicates a complex cooling history.

Pyroclastic Rock

A rock composed of volcanic ash, lapilli, or bombs that have been ejected and welded together.

Ash Flow Tuff

A pyroclastic rock primarily composed of ash particles (< 2mm).

Lapilli Tuff

A pyroclastic rock made of larger fragments like lapilli (2-64mm) and bombs (>64mm).

Glassy Texture

Non-crystalline texture that results from instantaneous cooling.

Obsidian

A dense, smooth glassy rock.

Pumice

A glassy rock that is very porous or 'frothy' due to trapped gas bubbles.

Vesicles

The holes in a volcanic rock created by gas escaping during cooling.

Felsic Rock

An igneous rock with a composition rich in feldspars and silica, typically light in color.

Mafic Rock

An igneous rock with a composition rich in magnesium and iron, typically dark in color.

Intermediate Rock

A rock that is between felsic and mafic, often with a 'salt-and-pepper' (50:50 light and dark) appearance.

Granite

A phaneritic (coarse-grained), felsic intrusive rock.

Rhyolite

An aphanitic (fine-grained), felsic extrusive rock.

Diorite

A phaneritic (coarse-grained), intermediate intrusive rock.

Andesite

An aphanitic (fine-grained), intermediate extrusive rock.

Gabbro

A phaneritic (coarse-grained), mafic intrusive rock.

Basalt

An aphanitic (fine-grained), mafic extrusive rock.

Obsidian and Pumice Composition

According to the classification chart, both are classified as felsic.

Tuff and Volcanic Breccia Composition

According to the classification chart, both are classified as intermediate.

Porphyritic Intermediate Rock

The full rock name for a rock with a porphyritic texture and an intermediate composition is porphyritic andesite.

Porphyritic Felsic Rock

The full rock name for a rock with a porphyritic texture and a felsic composition is porphyritic granite.

Mafic composition

A composition rich in magnesium and iron, typically resulting in darker-colored rocks.

Extrusive igneous rocks

Rocks that form from lava that cools quickly at or near the Earth's surface.

Intrusive igneous rocks

Rocks that form from magma that cools slowly beneath the Earth's surface.

Potassium feldspar

A type of feldspar that is rich in Potassium (K).

Plagioclase feldspar

Feldspars that are part of a solid solution series between Na-rich and Ca-rich endmembers.

Na-rich plagioclase feldspar

Albite.

Ca-rich plagioclase feldspar

Labradorite.

Mafic rocks

Rocks that include minerals such as Augite.

Intermediate rocks

Rocks that commonly include minerals such as Hornblende.

Primary minerals in granite

Potassium Feldspar, Quartz, and Na-rich Plagioclase (Albite).

Primary minerals in gabbro

Ca-rich Plagioclase (Labradorite) and Augite (Pyroxene).

Rock characteristics

The overall physical characteristics of a rock, based on its mineralogy and texture.

Mafic lava eruption

An eruption associated with low-viscosity lava that flows easily.

Shield volcano

A type of volcano built from layers of mafic lava flows from effusive eruptions, resulting in a broad, gently sloping structure.

Felsic magma eruption

An eruption associated with silica-rich, highly viscous magmas that trap gases.

Composite cone (stratovolcano)

A type of volcano built from alternating layers of lava and pyroclasts from explosive eruptions, resulting in a steep structure.

Extrusive equivalent of granite

Rhyolite.

Intrusive equivalent of basalt

Gabbro.

Intrusive equivalent of andesite

Diorite.

Extrusive equivalent of diorite

Andesite.

Rock with visible coarse grains

An igneous rock with visible, coarse grains of quartz, potassium feldspar, and biotite is called Granite.

Dark-colored fine-grained rock

An igneous rock that is dark-colored and fine-grained, with some visible vesicles is called Vesicular Basalt.

Glassy igneous rock

An igneous rock that is black, glassy, and shows conchoidal fracture is called Obsidian.

Salt-and-pepper appearance rock

An igneous rock that has a salt-and-pepper appearance with visible, interlocking crystals is called Diorite.

Light-colored fine-grained rock

A light-colored, fine-grained rock with large, visible crystals of quartz embedded within it is called Rhyolite.

Brittle tenacity

The tenacity of a mineral like quartz that will break when strong force is applied.

Malleable tenacity

The tenacity of a mineral like copper or gold that can be hammered into a shape.

Andesite Porphyry

An example of an igneous rock with a porphyritic crystalline texture and intermediate composition.

Aphanitic (fine-grained) texture

Extrusive rocks that cooled rapidly at or near the surface

Phaneritic (coarse-grained) texture

Intrusive rocks that cooled slowly at depth (Plutonic Rocks)

Porphyritic texture

Two grain sizes (large phenocrysts in a fine matrix) reflecting initial slow cooling followed by faster cooling near the surface

Obsidian

Glassy texture characterized by smooth glass with conchoidal fracture

Pumice

Glassy texture that is very porous (appears 'frothy') and can float on water

Tuff

Pyroclastic rock composed mainly of Ash (fragments $<2\text{mm}$ in diameter)

Diorite

Phaneritic (coarse-grained) crystalline rock of intermediate composition

Granodiorite

Intrusive rock composed of Na-rich Plagioclase, Quartz, Orthoclase, Amphibole, and Biotite

Felsic magma

Silica-rich magma (70% light minerals, 30% dark minerals) that is highly viscous and leads to explosive eruptions

Explosive Eruption Landforms

Steep composite cones or stratovolcanoes, sometimes calderas

Pyroclastic material fragments $>64\text{mm}$ in diameter

Volcanic bombs

The three types of Sedimentary rock textures

Clastic, Bioclastic, and Crystalline

Clastic sediment size range for Cobble, Pebble, Granule

Gravel (4mm to 256mm particle diameter)

Clastic rock made of angular gravel fragments

Breccia

Clastic rock composed of silt/clay with fissile property

Shale

Bioclastic rock formed from microscopic calcareous ($\text{CaCO}_3$) organisms

Chalk (effervesces with dilute HCl and scratches with a fingernail)

Crystalline rock composed of the mineral halite ($\text{NaCl}$)

Rock Salt (Exhibits 3-D cleavage at 90° angles and has a salty taste)

Grain characteristic produced by high energy transport (like ice or gravity)

More angular fragments (Poorly sorted)

Geologic principle stating that rock strata in lower layers are older than those in higher layers

Principle of Superposition

Feature of sedimentary rocks consisting of parallel layers separated by bedding planes

Strata, or beds

Metamorphic environment characterized by high heat and confining pressure

Contact Metamorphism (Produces non-foliated rocks)

Metamorphic environment associated with directed pressure (squeezing between plates)

Regional Metamorphism (Produces foliated rocks)

Non-foliated metamorphic rock derived from Quartz sandstone

Quartzite (Grains are deformed and fused)

Non-foliated metamorphic rock derived from Limestone

Marble (Effervesces with weak HCl)

Foliation type characterized by alternating bands of light (felsic) and dark (mafic) minerals

Gneissic Layering

Metamorphic grade associated with Gneissic Layering (Gneiss)

High grade

Foliation style characterized by a parallel arrangement of macroscopic, platy minerals like mica

Schistosity