How do I find out what the name of a rock is?

Question

The rock is dark and it appears to be coarse-grained with pieces of quartz in it.

Answer 1

It sounds like a plutonic igneous rock (coarse-grained suggests it cooled slowly, underground) or perhaps even a metamorphic one? Ae you sure the mineral you're seeing is quartz? If it's just a white-colour it may be plagioclase... Quartz is generally found in the more felsic igneous rocks such as granite, but you say that the rock is dark - with granites the overall rock usually looks quite light in colour cause it has so much plagioclase, quartz and muscovite - though it does usually have dark specks of minerals such as biotite and hornblende, they don't usually make up the majority of the rock! Is there any chance you could be mistaking olivine for quartz? Olivine looks kind of green and glassy rather than clear and glassy... in this case it could be a gabbro? You may like to use google images to look at pic of granite, diorite, gabbro etc, because unless you're able to post a link to a photo of your rock, it's very difficult to guess what it could be!
Hope I've helped a little, anyway :)

Answer 2

Make a thin section and study the petrography of the rock. Identify the mineral constituents and texture. A dark coarse grained rock with quartz is not very common.
In hand specimen, try to identify the dark minerals. Also check whether those quartz grains are primary of secondary. A dark coloured coarse grained rock is commonly a basic or an ultramafic plutonic rock. And hence presence of quartz is unlikely, they may be some other mineral

Answer 3

Granite?