Rock Types
(Bolded are names of rocks you must know for the practical)
Igneous: formed from melted rock
Characteristics to look for:
Crystals- evenly distributed (not squashed)
Large- cooled slowly (intrusive-underground magma-tend to
be lighter colored)- granite
Small- cooled fast (extrusive -above ground lava-tend to be
darker colored)- basalt
Glassy –obsidian (extrusive)
Lots of air holes from gasses escaping (like pop bottle release)scoria and pumice (extrusive)
Hard and fairly dense
Sedimentary: formed from erosion, deposition and compaction
Characteristics to look for:
Layers:
Mechanical sediments made of particlesEroded rock grains (listed smallest to largest grains)
Clay-claystone or shale
Silt-siltstone or shale
Sand-sandstone
Pebbles or larger rocks- Conglomerate (like natural
cement)
Biological SedimentsFossils or ground fossils-limestone
Plants-coal or oil (fossil fuels)
Chemical sediments- Dissolved in water and left behind after water
evaporated
Pure mineral crystals- gypsum, calcite, halite
Replaced other, softer minerals – chert
(flint-black/grey, jasper- red/orange)
Tend to be softer-more easily scratched, leave hands “dusty”
Tend to be Less dense rocks
Layers
Not usually Glittery
Metamorphic : Formed From Heat and pressure
Characteristics to look for:
“zebra stripe” banding (light and dark due to “crunchy peanut
butter” effect- some minerals are softer than others)Gneiss (pronounced “nice”)
“Glittery” layers – Gneiss or Schist
Cracked, ‘Glazed donut”- Quartzite
More dense and harder than sedimentary rocks
Fused layers (has a sheen) - Slate
Squashed crystals-glitter Gneiss or Schist
Folding or twisting of layers or bands (evidence of pressure)
Rock type
Becomes
Shale

Sandstone or quartz 
Granite

Mica or basalt

Limestone

Metamorphic type
Slate
Quartzite
Gneiss
Schist
Marble
Note: Fossil shells, limestone and marble are all made of CaCO3
(Calcium Carbonate) and will bubble or fizz when acid is applied.