Possible Alexandrite?

Thanks Lizc for the trust placed on our forums. The thread on Alexandrites started on May 21st 2014 by Gemlite generated an extensive discussion, citing alexandrites of different countries of origin that appeared at public auctions conducted by Christie's and Sotheby's over the years, and went on till around the end of August 2014. The discussion brought out the salient features of Alexandrites from source countries such as Russia, Sri Lanka and Brazil and also established a market ranking for alexandrites based on country-of-origin, which goes as :- Russia - Brazil - Sri Lanka - Others. According to this discussion the average price-per-carat value of Russian alexandrites vary between US$50,000-US$70,000. The PPC values of Brazilian alexandrites vary between US$20,000-US$50,000 and those of Sri Lanka alexandrites between US$5,000-US$20,000.

It is highly unlikely that your gemstone is a color-change diaspore or a color-change fluorite. Color-change diaspores are a recent discovery from Turkey in the 1990s, but the ring incorporating your color-change gemstone had existed in your family in the late 60s or early 70s. Color-change fluorites have a low hardness on the mohs scale and good cleavage properties and hence their use in jewelry is limited. If at all they are used in jewelry they can be set only on pendants and earrings, which are not subjected to wear and tear like rings and bracelets. Your piece of jewelry is a ring, and hence it is unlikely that the stone set in the ring is a soft fluorite.

We are now left with three options - alexandrite, color-change sapphire and color-change garnet, whose hardness is respectively 8.5, 9.0, and 6.5-7.5 on the mohs scale, and all of which are used on ring settings. According to you the color change in your gemstone is from a teal blue color in natural daylight to a purple color in indoor lighting. I hope by indoor lighting you mean incandescent lighting and not fluorescent lighting. I have also noticed a brown color associated with the purple color in image 3 you have uploaded. If this is a true brown color associated with the stone in incandescent lighting and not a reflection of its background, the color of the stone in incandescent lighting can best be described as brownish-purple.
Blue to Purple color change from natural daylight to incandescent light are found in some alexandrites originating from Brazil; rare variety of color-change sapphires and color-change garnets from some countries. Pyrope-spessartite color-change garnet found in the Umba Valley of East Africa change color from greenish-blue in daylight to reddish-purple in incandescent light. Color-change garnets from Bekily, Southern Madagascar change color from blue in natural daylight/fluorescent light to red/purple in incandescent light. Sri Lanka color change garnets change color from blue/green/gray in natural daylight to reddish-purple in incandescent light. Out of the three color-change gemstones - alexandrite, sapphire and garnets - the rarest is the color-change sapphire. The occurrence of alexandrites and color-change garnets are also rare but not so rare as color-change sapphires. Hence, your gemstone Lizc is most probably an alexandrite or color-change garnet and not an extremely rare color-change sapphire. If the gemstone is an alexandrite, based on the color change you have observed (blue to purple), the alexandrite is probably of Brazilian origin, but not from Hematita mine where alexandrites were discovered only in 1987. If there is a tinge of brown in the colors you have observed the alexandrite is most probably of Sri Lankan origin. If the gemstone is a color-change garnet, it can be either from the Umba Valley where gemstone deposits were discovered in the mid 1960s or Sri Lanka the oldest source of gemstones of several varieties including garnets. It cannot be a Bekily color-change garnet where such stones were exploited only in the late 1990s.