FIBROLITE (Sillimanite)
Very rare; hard, but very easily cleaved and few attempts to cut succeed; as waterworn transparent pebbles in gem gravels of Burma; collectors’ stone only.
Burma, facet-grade pebbles, 2-10 ct.    ct.    1.00-2.50
FLINT,   See   QUARTZ FLUORITE
Soft, cleavable, low refractive index, but occurs in many attractive hues and is commonly faceted for collectors; massive purple and white banded variety from England, known as “blue John,” has been extensively employed for or¬namental objects of considerable size, but the source of material appears de¬pleted and the industry dormant. Facet grade available in colorless, pale blue green, purple, yellow, and, rarely, in pink or red; cut gems to several hundred ct.
England, green, purple, fine, 10-100 ct.    gm.    .20-.30
Illinois, purple, yellow, fine, 100 ct.+    gm.    .05
Mexico, pale green, to 50 ct.    gm.    .20-.30
New Hampshire, fine green, to 200 ct.    gm.    .05-.35
Ontario, pale green, to 50 ct.    gm.    .25-.65
S. W. Africa, pale green, to 100 ct.    gm.    .05-.10
FRIEDELITE
Extremely fine-grained massive material from zinc mines of New Jersey; translucent; some resembles brownish carnelian in color; for cabochons and translucent faceted gems;  rare except at localities named;  a collectors’  gem.