Kyanite is a metamorphous mineral that occurs in schists and granite pegmatites. Gem-grade kyanite is extremely rare. Its name comes from the Greek word kyanos which means blue. Kyanite is an aluminum silicate that comes in various colors. Blue Kyanite is by far the most valuable variety. Kyanite is allochromatic, meaning it has color-zoning, just like some sapphires. Kyanite is relatively soft - from 4 on the Mohs scale to roughly 6 depending on the direction (perpendicular or parallel to its long axis).
Grandidierite crystals have been since found in Malawi, Namibia, and Sri Lanka. However, gem-quality grandidierite, with rare exceptions, has been found only in Madagascar.
Grandidierite rarely exceeds 3-4 carat; the gem-quality stones are mostly under one carat, often heavily included.
Grandidierite has two cleavage planes making it susceptible to breaking during the cutting. It also suffers from strong trichroism, making it difficult to orient during cutting to make sure it faces blue or bluish-green.
Fluorite has formed 250 and 100 million years ago from hydrothermal solutions that filled underground fissures. Due to its softness and perfect cleavage fluorite is a challenging gemstone to facet and polish.
Most fluorites have pale pastel shades of pink, yellow, and that special hue we call "a newborn surprise." However, occasional specimens can rival the deep purple color of amethyst. Braldu fluorite is another variety with an unusual bright apple-green color. Fluorite can also display distinctive bi-color and multi-color zoning.
The ‘Blue John’ variety with curved bands of blue, purple, yellow, and white, and was used in England to carve ornaments since Roman times.
Andalusite is a cute brown-green gemstone first discovered in Andalusia, Southern Spain. Andalusite is strongly pleochroic; its color is directional and depends on the direction of view. Andalusite is polymorphous with kyanite and sillimanite, meaning they share chemistry but not a crystal structure.
Iolite's name comes from the Greek ios meaning violet, not iPhone operating system. Iolite has different colors in different directions in the crystal - a property called pleochroism. From one direction a crystal can look sapphire-like violet-blue, from the other it can be completely colorless, and still a brownish-yellow from the opposite side. The Vikings looked through iolite chips to determine the exact sun position using iolites as primitive polarizing filters to aid navigation.
Call it "fools' Paraiba," apatite, is a gemstone that exists on the fringes of the jewelry world because of its softness. It is rarely found in sizes larger than one carat and is mostly unknown to the general public. Apatite comes from Brazil, Mexico, and Madagascar. Fine gem apatites with a “neon” blue-green color similar to Paraíba tourmalines or vivid-purple specimens from Maine are prized for their rich hues.
Sunstone comes in various warm shades ranging from colorless to yellow, orange, brown, pink, red, green, blue-green, and even multicolor. Sunstone's glistening appearance from certain directions is called schiller from the Old German word scilihen, which means to wink or blink. The color is determined by the abundance and size of copper platelets within the gemstone. In the US, there is plenty of sunstone in Oregon. However, it also has been found in Southern Norway, Sweden, and South Australia.
The gemstone was discovered in 1883 on Mt. Soktui in Siberia by Russian geologist and Romanov's tutor Pavel Jeremejev. Currently, jeremejevite is the rarest gem coming from Namibia. Although found in many places, the specimens from Namibia come in pretty Paraiba-like light blue hues. The gemstone does not have cleavage and is pretty durable; its hardness is 6.5 - 7.5 on the Mohs scale.
Painite is a deep-red or brownish-red stone that was found in Mynamar in the 1950s. Until 2001, only three painite crystals were known to exist. For decades the political difficulties in Myanmar prevented exploration and mining. Since then, additional discoveries have produced more specimens, but the gem-quality material remains extremely rare, exceeding the per-carat of the finest Burmese rubies.
Although the painite has a hardness of 8 combined with excellent brilliance and attractive red color, it is typically heavily included and fractured. As a result, most painites are cut small and shallow, which reduces their brilliance.
Taaffeite, a rare gemstone that looks similar to spinel, comes in various pink and purple shades like lilac, violet, mauve, red, brown, gray, green, and colorless.
Edward Taaffe discovered taaffeite in 1945 in a box of spinels. Only a handful of taaffeite gems have ever been found, mostly in Sri Lanka and Tanzania.
Taaffeite was long mistaken for spinel, which is very similar, but taaffeite's birefringence sets them apart.
Danburite was discovered by Charles Upham Shephard (1804-1866), an eminent American mineralogist who was a professor of natural history at Amherst College for many years. Shepard began his career as an assistant to Benjamin Silliman at Yale University. Danburite is usually colorless to very light pink, but some deposits may produce specimens in shades of light yellow or brown. Danburite is known for its excellent transparency and clarity.
By chemical composition, danburite is a calcium aluminum borate silicate. It is quite hard, with a rating of 7 to 7.5 on the Mohs scale. Since it has a reasonably high refractive index (6.30 to 6.36), in the same range as tourmaline, the material can be faceted with good results. Danburite has very little cleavage, so cutting the gem is not a problem for an experienced lapidary. Danburite's density is 2.97 to 3.03, about the same as jadeite.