Volcanic Rocks:  Review Sheet

I.  Magma Composition

            Enter relative values (low, intermediate, high)

	Basalt	Andesite	Rhyolite
SiO2	Low (50%)	Intermediate (60%)	High (70%)
Fe, Mg	High	Intermediate	Low
Ca	High	Intermediate	Low
Na, K	Low	Intermediate	High

II.  Rock Textures

            Enter relative crystal size (coarse, fine), cooling rate (slow, fast), and indicate whether the rock type is intrusive or extrusive

TeXTURE	Crystal size	cooling rate	intrusive/ extrusive
Phaneritic	Coarse	Slow	Intrusive
Aphanitic	Fine	Fast	Extrusive
Porphyritic	Coarse/fine	Slow/fast	Extrusive
Pumiceous	None (frothy)	Very Fast	Extrusive
Glassy	None	Very Fast	Extrusive

III.  Mineral Assemblage                             

            Enter the names for extrusive and intrusive rock types corresponding to each of the three mineral assemblages

MINeral assemblage	EXTRUSIVE ROCK	INTRUSIVE ROCK
"Dark"	Basalt	Gabbro
"Intermediate"	Andesite	Diorite
"Light"	Rhyolite	Granite

IV.  Pyroclastic rock textures                      

            Enter the names for each of the pyroclastic rock types.

Size	Tephra name	pyroclastic rock name
< 2mm	Ash	Ash tuff
2 – 64 mm	Lapilli	Lapilli tuff
> 64 mm	Bombs/blocks	Agglomerate