This ain’t the Flintstones we’re
talking about.
 All
rock begins as Magma.
 Magma is molten rock formed beneath
the Earth’s crust.
 As magma cools, the molecules
crystallize and the material solidifies.
 Igneous (“formed by fire”) rock is the
result of this process.
 Igneous rock is composed, primarily, of
silicate material.
 Fine-grained
and Coarse-grained texture
are descriptions based on the size of the
embedded crystals.
• Fine-grain is rapidly formed near the surface.
• Coarse-grain is slowly formed deep below the
surface.
 Porphyritic
texture is a mix of fine- and
coarse-texture.
 Glassy-texture is formed when ejecta is
thrown into the atmosphere and cools
rapidly.
 Sedimentary
rock is formed when
weathered igneous rock is formed into a
new conglomerate due to compaction
and/or cementation.
• Compaction is caused by deposition of material
resulting in burial and immense pressures force
crystals to intertwine.
• Cementation is caused by additional materials,
which possess adhesive qualities, binding the
material together.
 Detrital
– originate from solid particles of
weathered igneous rocks.
• Based on particle size.
 Chemical
– formed from material carried
in solution to lakes and seas.
• Salt – deposited from salty seas.
 Limestone
– from exoskeletons of marine
invertebrates.
 Coquina and Chalk
 Travertine
limestone – typically
deposited in caves from dripping action
of water.
 Coal – not formed from minerals, but
from remains of pre-historic organisms.
 Compaction
and Cementation
 Strata – “layers”
 Metamorphic
means “changed in form”.
 Can be formed from igneous,
sedimentary, or other metamorphic rock.
 Slight changes are termed low-grade
metamorphosis. (Shale to Slate)
 Drastic
changes are termed high-grade
metamorphism.
 Three agents of metamorphosis –
• Heat – the most important agent. The heat energy
causes chemical changes whereby crystals
reconfigure. Likely to happen very deep in Earth’s
crust.
• Pressure – also happens deep in Earth’s crust.
Omnidirectional pressure compacts rock in all
directions. Folding (previous slide) is graphic
representation.
• Chemically-active fluids – the most common is water.
Water allows ions to move about in pore-spaces in
rock and crystals can be changed.
 Foliated
Rocks – derived from shale and
can be split along plate lines. Examples
include Slate, Schist, and Gneiss.
 Non-foliated
Rocks – derived from
limestone and will fracture under force.
Examples are Marble and Quartzite.
 Many
metallic mineral resources are
igneous and metamorphic.
 Ores of chromium, magnetite, and
platinum settle out in heavier deposits in
magma chambers. (Igneous)
 Ores of gold, lead, zinc, and silver are
formed from hydrothermal solutions.
(Metamorphic)