What is a Rock?
 A naturally occurring solid
combination (aggregate) of one or
more minerals.
 3 Types of rocks:
 Igneous
 Sedimentary
 Metamorphic.
Minerals
 Occurs in nature inorganically with specific chemical
properties and a definite structure.
 There are over 4,900 known mineral species.
 Minerals are distinguished by physical and chemical
properties.
 Minerals have color, luster, streak, hardness, cleavage,
fracture and specific gravity (density).
Mineral Shapes:
Gems
 Gems are visually attractive and rare minerals. The brighter the gem the
more desirable it is.
 A gem is precious or semi-precious and if cut and polished can be used
for jewelry.
 The 4 precious gems: diamond, ruby, sapphire, emerald.
 Semi-precious gems: amethyst, amber (organic), pearls (from sea
creatures), garnet, aquamarine, topaz, peridot, garnet, topaz,
turquoise, etc.
 Most birthstones are gems: diamond, amethyst, sapphire, ruby, etc.
 $$$$$$$$$$$$$$$$$$$$$$$$$$
Three Types of Rocks:
 Igneous:
 Crystallization of magma or lava.
 Latin for “fire”.
 Sedimentary:
 Formed at or near the earth’s surface by an accumulation of
particles (small or big).
 Latin for “settling”.
 Metamorphic:
 Result of igneous, sedimentary or metamorphic rocks
“changing” from high heat and pressure.
 Greek for “change form”.
Igneous
 Intrusive/plutonic – formed under the earth’s surface.
 Course grained, cools slowly, hard, crystal texture, no banding
or layering
 Extrusive – formed above the earth’s surface.
 Fine grained or smooth, cools quickly, no banding or layering.
 Felsic – usually light in color and has high silica content
with quartz.
 Mafic – usually dark in color and has low silica content,
high in iron and magnesium.
 The heat from the earth comes from gravity and pressure
deep underground, and also mostly from radioactive decay.
Sedimentary
 As particles settle, pressure causes the material to
become compacted or cemented.
 Clastic/Detrital – formed from an accumulation of
fragments of pre-existing rocks and minerals.
(conglomerates).
 Organic – formed from the action of plant and animal
remains (mud rocks, coal).
 Chemical – nonclastic, from a saltwater or water
solution that is concentrated and what is left after the
liquid evaporates (limestone).
Metamorphic
 The most complex group of rocks.
 Through heat, pressure, and chemical processes deep
underground, the mineralogy, texture and chemical
composition of the rock changes.
 Foliated – has layering or banding
 Schist has layering, ancient Greek “split”, schistose fabric, has
schistosity, fissile (splitting in thin layers), mica or
horneblende are aligned and elongated > 50% makeup.
 Gneiss (pronounced nice) has banding, mica or horneblende are
aligned and elongated < 50% makeup.
 Non-foliated – no layering or banding (marble, quartzite).
The Rock Cycle
Links that Rock!
 http://geology.com/rocks/
 http://geology.about.com/od/rocks/a/Rock-
Tables.htm
 And for some GREAT bumper stickers…….
 Sources: geology.com, wikipedia, Prentice Hall Science Book, Mariam-Webster.
Schist
Happens!