Some basic gemstone properties.

Gemstone Properties.
Some basic info, there are many sites on the internet with more detailed information, this is just a starting place for your further research.

Hardness, the scale for hardness is the Moh's scale from 1 to 10 with talc being 1 and diamond being 10.
The Moh's scale presumes that if one type of mineral can scratch another then it is harder and vise versa.

Most dust we encounter is comprised of Silicon Oxide (SiO2) and has a hardness of 7, this is what scratches everything.

Most gemstones cut are generally of a hardness of 7 or above otherwise they would just get scratch, quart based gems are a 7, for example Smokey Quartz, Citrine, Amethyst to name a few.
There are some gemstones that are cut with a hardness of only 6 but they scratch and wear too easily with most of the dust they encounter.

Some opal another SiO2, is only a 6 even though its rated at a 7, some opal is also harder than 7, Mintabe opal for example is extremely hard, you can feel the different hardness when you cut it.

Fracture and cleavage are good indicators as to gemstone identity.
Fracture is the way the stone splinters, in Quartz for example the fracture is conchoidal (shell like) in that the mark left looks sort of like a sea shell. (use your imagination)
Cleavage is the way the stone slits along the crystal growth lines, Topaz for example cleaves flat and resembles a sheet of glass when split.

Moh's scale of hardness and common gemstones you may come across in your travels.
Quartz, Opal, Zircon 7
Beryl, Aquamarine, Emerald 8
Topaz 8
Corundum, Sapphire, Ruby 9
Diamond 10

Topaz and quartz, telling apart can be difficult, one trick is to hold the stone to your cheek, topaz always feels cold no matter the temperature.