Gemstones and mineral specimens have many properties. One that is particularly important for jewelry is hardness. Why? A stone that is soft should not be used in an unprotected setting or in a piece that is likely to be bumped.
For example, I had a lovely opal ring with four opal cabochons in prong settings. Not realizing at first how fragile opal can be, I wore the ring regularly. It didn’t take long before I’d chipped one of the stones. I was slightly more careful with it but still managed to chip a second stone and lose that first one (as it was loose in its setting). Fortunately, we were able to match up the opal, cut and polish new cabochons and restore the ring completely.
For stones that are below 7 on the Mohs’ hardness scale, dust can do some damage if rubbed into the stone as quartz particles are fairly common in dust. To help identify how hard a stone is, there is a “simple hardness tester” that can be used as a guide and to provide an idea of what the various scale values mean along with an example in parenthesis:
1 (talc) and 2 (gypsum): can be scratched with a fingernail
3 (calcite): can be scratched with copper coin
4 (fluorite): easily scratched with knife
5 (apatite): can be scratched with knife
6 (orthoclase): can be scratched with steel file
7 (quartz): scratches window glass
8 (topaz), 9 (corundum), 10 (diamond) : no simple test
I would not recommend actually trying any of the scratch tests on finished stones but rather use the information to help understand what the various Mohs values represent. Note that the scale is relative, so that the difference between a 4 and 5 on the scale is not the same as the difference between 9 and 10.
 Gemstones of the World: Newly Revised & Expanded Fourth Edition by Walter Schumann, p20 (based on the table “Relative and Absolute Hardness Scale”)
Asterism is a term which describes “the effect of light rays forming a star (Latin aster, star)…It is usually created through reflection of light by thin fibrous or needle-like inclusions that lie in various directions.” 
Stars in gemstones may have four, six, or (less frequently) twelve rays. With these stones, the angle of the stone to a light source is important to be able to see the star. Natural gemstones known to exhibit asterism include:
star rose quartz
star blue quartz
 Gemstones of the World: Newly Revised & Expanded Fourth Edition by Walter Schumann, p.52
Tourmalinated (tourmaline included) quartz is a type of quartz that has black or green tourmaline needle-like inclusions within it. The stone looks best when the quartz is clear but more common specimens are found where the quartz is whitish-grey. This uniquely patterned stone has a Mohs hardness of 7, so it is moderately hard but can scratch and get chipped.
Clean your tourmalinated quartz jewelry with water mixed with a small amount of mild liquid hand soap with a soft cloth, rinse with water and dry with a soft cloth. I have a sterling silver and tourmalinated quartz bracelet that I’ve been wearing for 3 or 4 years – the round stones have been unaffected by bathing soaps or shampoo, still looking as lovely as the day I made the bracelet.
Tourmalinated quartz has multiple metaphysical associations with it, including:
excellent protective stone
brings balance and inner strength
deflects and grounds negativity
reduces anxiety and depression
Below is a photo of a tourmalinated quartz trillion. We have a variety of loose gemstones as well as lovely completed pieces at www.dragondreamsjewelry.com.
“Beads of quartz have been found in caves in Israel that were occupied between 5,000 and 6,000 years ago.” Clearly quartz has been valued over time as a stone of worth for adornment.
There are many varieties of stone in the quartz family. Many are commonly known as quartz: rose quartz, smoky quartz, blue quartz, milky quartz, tourmalinated quartz, rutilated quartz, strawberry quartz, amethyst, and even citrine. However, there are still others less commonly known to be quartz.
Aventurine – usually a milky medium to dark green colored stone but it may be a metallic orange-brown color
Dumortierite quartz – a rare violet-blue to denim-blue colored stone
Prasiolite – a pale green stone that may be anywhere from transparent to translucent; most prasiolite is created by heating amethyst or citrine
Tiger’s eye/hawk’s eye – tiger’s eye has brownish yellow – golden brown/green colors while hawk’s eye has darker blue/black colors; both have the “cat’s eye” effect (chatoyancy) because of the way quartz filled in for the asbestos in the rock fibers as the stone formed
 The Jeweler’s Directory of Gemstones by Judith Crowe, p.67