27 March 2019

AUGUST BIRTHSTONES – SPINEL The Black Prince’s Ruby. The Timur Ruby. For centuries, spinel, the great imposter, masqueraded as ruby in Europe’s crown jewels. Until recently, spinel was an underappreciated gem with little consumer recognition. Increasing demand for ruby alternatives rekindled appreciation for spinel’s rich red color and history. In ancient times, southeast Asia’s mines yielded exceptional large spinel crystals, which became the treasured property of kings and emperors, often passing through many hands as spoils of war.
Mineral: spinel;
Chemistry: MgAl2O4;
Color: red, orange, pink, purple, blue, black;
Refractive index: 1.718;
Birefringence: None;
Specific gravity: 3.60;
Mohs harness: 8;
COLOR: The most valued spinel colors are bright red, cobalt blue, and vivid pink and orange. Pale lavender is more affordable;
CLARITY: Spinel with no visible inclusions is preferred. The more prominent the inclusions, the less valuable the gem;
CUT: Spinel is most often cut in cushion and oval shapes. When properly proportioned it has excellent brilliance;
CARAT WEIGHT: Fine-color spinel is rare above five carats. Most fine-quality rough is cut to non-standard sizes to save weight;
AUGUST BIRTHSTONES – PERIDOT Found in lava, meteorites, and deep in the earth’s mantle, yellow-green peridot is the extreme gem. The ancient Egyptians mined peridot on the Red Sea island of Zabargad, the source for many large fine peridots in the world’s museums. The Egyptians called it the “gem of the sun.” Today this gem is still prized for its restful yellowish green hues and long history. Large strongly-colored, examples can be spectacular, and attractive smaller gems are available for jewelry at all price points.
Mineral: Olivine;
Chemistry: (MgFe)2SiO4;
Yellowish green;
Refractive index:
1.65 to 1.69;
0.035 to 0.038;
Specific gravity:
Mohs harness:
6.5 to 7;
Although the best peridot is a pure grass green, most peridot is yellowish-green;
Most fine peridot is eye clean. Tiny black spots might be visible with magnification;
Peridot is cut in a wide variety of styles, including ovals, emerald cuts, and cushions;
Large crystals of peridot have cut gems more than 50 carats in size~27.jpg