Rock with only feldspar and quartz?

Question

what would be the name of an intrusive igneous rock with only quartz and feldspar? My geology teacher didn't have a clue

Answer 1

rock man,

The most probable answer to your question is granite, but there are several other categories of rock (that need only contain quartz and feldspars) that are considerably less common. It depends on the relative amounts of quartz, alkali feldspar, and plagioclase feldspar. If you click the link below and find your rock's approximate composition on the upper half of the diagram, you can get a geologically exact answer to your question:

http://en.wikipedia.org/wiki/QAPF_diagram

Another possible answer is pegmatite. A pegmatite is a granitic rock that crystallized very slowly inside the earth and formed large crystals. It is more of a textural term, and is used when the crystal size is quite large. Because these minerals are the last to crystallize, the cores of pegmatites often contain only quartz and feldspar.

Answer 2

Syenite is undersaturated in silica meaning no quartz or an particularly little quantity. relies upon on how choosy you want to be yet via definition syenite skill no quartz seen. so because it rather is incorrect. Granite is right. and because each little thing that had those 2 minutes is frequently lumped as granite i might say granodiorite is the subsequent suited suited. greater valuable then syenite in any case.

Answer 3

I would think that this would be classified as a granite, at least a granitoid (which is a granitic like rock that includes some siliceous diorites). All granites have quartz, orthoclase and plagioclase, and almost always biotite mica. Were there flecks of black flat biotites in the rock? If not, you might have something weird that is super siliceous.

Answer 4

Depends on the relative amounts. Check this out for the double-triangle figure:
http://www.bccmeteorites.com/class.html

Ignore the bottom triangle with F-OIDS which are quartz-poor minerals and which you don't have since you have quartz.

When you figure it out post the answer as I am interested to know. Also, where is the rock from?