Question: How to you know what type of rock or crystal it is when you find them

Danny Hnatyshin answered on 7 Nov 2020:

There are a few different hings you can look at to figure out the type of rock or crystal you are looking at.

Crystals, or more accurately minerals, all have unique properties such as:
– How hard they are
– What colour they are
– How they break, known as fracture/cleavage, describes if they break into random pieces, cubes, or sheets
– How shiny/dull they are, known as lustre

In introductory geology courses you learn how to use different characteristics to find out how to identify minerals. For example the mineral quartz is identified as follows
Hardness: Will scratch glass (hardness is 7/10 on the hardness scale)
Colour: Typically semi-transparent white, grey, purple
Fracture: Smooth irregular surfaces
Lustre: Vitreous, which means it looks a bit like glass

For rocks you try and figure out what minerals make it and the patterns that the minerals make (do crystals align, random)
For example the rock granite is composed of the mienrals quartz (grey), feldspar (white/pink), biotite (black)