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
In previous posts, we’ve discussed both sapphires and rubies, which are varieties of corundum. This popular, colorful, and durable gemstone is highly prized.
Corundum is now being diffusion treated with titanium and chromium, where the stone is irradiated to get the colorant to absorb into the outer layer of the stone. Another treatment, beryllium diffusion, has been common for years. Stones treated with any of these methods may lose part or all of their color if the stone is damaged or repolished.
It is possible that there are health hazards from these stone treatments. For example, chromium is toxic and may damage DNA cells.  “There is disturbing evidence that suggests the beryllium treatment poses a health hazard to the workers who process and cut the gemstones and to the merchants who handle them.” 
Surprisingly, irradiated gemstones are generally considered safe because of the mandated cooling off period and monitoring requirements. “NRC [Nuclear Regulatory Commission] requires that the initial distribution of these stones be by a distributor licensed by the NRC. This distributor would conduct radiological surveys of each batch of gemstones to ensure that any residual radioactivity falls below regulatory limits.” 
Sellers in the United States are required by law to disclose all treatments to stones they sell.
Sapphire is believed to derive its name from the Greek σάπφειρος; sappheiros, meaning ‘blue stone’. However, there are a variety of possible word origins from Latin, Sanskrit, Hebrew, and other languages.
A 12th century writing by Abbess Hildegard von Bingen includes this use for a sapphire: “Who is dull and would like to be clever, should, in a sober state, frequently lick with the tongue on a sapphire, because the gemstone’s warmth and power, combined with the saliva’s moisture, will expel the harmful juices that affect the intellect. Thus the man will attain a good intellect.”
Sapphire is a variety of corundum which comes in a variety of colors, including pink, yellow, green, purple, blue, colorless (virtually any color except ruby, another variety of corundum which has a purplish-bluish red to yellow-red color.) Sapphire has a Mohs hardness of 9, making it quite durable and strong.
Clean your sapphire 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. You may want to use a toothbrush to clean under the stone. While sapphires are not particularly light sensitive, all colored stones can fade with prolonged intense exposure to sunlight, so be sure to store your sapphire jewelry out of direct light. As sapphire jewelry can last many years, periodically check the prongs and/or settings to be sure the metal is still holding the stone securely in place.
Because these beautiful stones are durable and colorful, there are many synthetics and imitations on the market. Heat treatment of sapphire has been a common practice since the 1960s . Most of the sapphires we have seen recently in chain jewelry stores have been lab created rather than natural stones. As always, be sure to ask your seller.
Some of the metaphysical properties associated with sapphire include:
bring clarity and clear perception
assist communication, including with the spirit realms
release mental tension
enhance creative expression and intuition
promote fairness and loyalty
protection during astral travel
Chakras (by color):
White, purple – Crown chakra
Blue – Third Eye and throat chakra
Padparadscha, Yellow – Solar plexus chakra
Green – Heart chakra
 The Jeweler’s Directory of Gemstones by Judith Crowe, p.48