Tip for emerald owners: clean your emeralds with a soft chamois or other cloth, using warm soapy water if needed. Do NOT use steam or an ultrasonic cleaner. Most emeralds are oiled and/or fracture filled and steam and ultrasonic cleaners can cause damage.
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”)
Because amethyst is one of the more popular stones, it seemed worth learning a bit more of how it was used throughout history. As the excerpts below highlight, amethyst was used for more than preventing drunkenness.
From A Lapidary of Sacred Stones by Claude Lecouteux, p47-48
“In the thirteenth century, it was said the amethyst prevented the devil from causing harm and preventd a person from seeing ‘ghosts’ (fantasme). It also provided protection from the entity known as a nightmare and from fevers, it granted riches, and made one humble, courteous, and gracious.”
“Etched with the moon and sun and hung around the neck with hairs from a cynocephalus* and feathers from a swallow, it protects one from evil spells. Its magical properties are increased if set in gold or silver and if a man on horseback holding a scepter is carved on it.”
* cynocephalus likely refers to some type of baboon
“If one finds an image of an amethyst of a man with a sword in hand seated on a dragon, and this stone is then set in a ring of lead or iron, the wearer will obtain the obedience of all the spirits, tnd they will revela where treasures are hidden and answer whatever questions he may ask.”
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
The origin of the term “opal” is unclear – it may be from the Roman word opalus, the Sanskrit úpala, the Greek opallios, or any of many other possibilities. In this way, the opal extends its mystery beyond the well known color play into the name of the stone itself.
Natural opal has a lot of variety, including: white opal, black opal, jelly opal, boulder opal, opal matrix, fire opal, harlequin opal, crustal opal, Andean opal, Ethiopian opal, and common opal. White and black opal are most commonly found and these typically display the gorgeous color play which from “the diffraction of light off tiny, closely packed silica spheres inside the stone.”  The silica gel inside the stone is 5-30% water. Most of the world’s natural opals today come from Australia – particularly Lightning Ridge (black opal) and Cooper Pedy (white opal).
Because opal is soft (5.5-6.5 on the Mohs scale), it is often sold as doublets or triplets, which provide color enhancement as well as some protection for the stone. There are also synthetic man-made opals, like Gilson opal and opalite. Be sure to ask your seller for information about any stone you purchase.
Opal can be easily damaged by pressure and impact. Opal is also sensitive to acids and alkalis because of its porous nature, which also makes it vulnerable to perfumes, soaps and detergents. Jewelry should always be removed before washing or applying lotions and other similar products.
If an opal is allowed to dry, it will crack and craze. In most cases, opals do not need any special care while stored. However, if you live in a very dry climate, or keep opals in a dehumidified room, some precautions are necessary. Keeping them in a tight plastic bag, with a damp piece of cotton or fabric will prevent dehydration.
Opals do not mind being hot or cold, it is the rate of change that damages them. You need to avoid exposing the stone to a sudden change in temperature, like from a warm house to the winter’s cold. Simply wearing an opal under clothing will protect it.
Clean your opal with warm or room temperature soap and water. Avoid wearing the stone where it will get rough treatment.
According to lore, opal helps relieve issues with eyesight and was believed to obscure its wearer with a thick fog. 
There are other metaphysical properties ascribed to this multi-colored gem:
Makes it easier to handle changes in life
Protects the wearer from harm
Supports renewal and fidelity in love
Intensifies emotions and intuition
Helps to express your true self
Chakras: links the root and crown
 The Jeweler’s Directory of Gemstones by Judith Crowe, p.92
 A Lapidary of Sacred Stones by Claude Lecouteux, p.244
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