Some basics to know while learning about crystals may help you to determine which crystals have similar properties to others, and which ones are useful for reasons relating to the chemistry of the crystal, or its structure or formation process.
Many of the crystals we use are quartz based, that is, silicon dioxide SiO2.
Many more are cyclosilicates, which are more complex molecules of silicon and oxygen, and further complex chains and cycles of silicon and oxygen from subsets of the silicate families.
Then, adding to this the various elements in nature, like aluminium compounds which become feldspar. This then becomes the basis of other crystals using a variety of elements like calcium, magnesium, manganese, berilium, potassium, sodium and chromium, to name a few.
Having looked at the chemical structures, there are things to consider like the way the crystal was formed, quickly or slowly, from the volcanoes or in the creek bed.
The complexities are enormous, but for crystalaholics I’ve broken it down into more manageable bites sizes.