transparent crystals of Sillimanite come from Mogok, Burma (Myanmar); and from the Ratnapura District, Sri Lanka. Orissa, India, is another uncommon source for transparent crystallized Sillimanite.
In the U.S., brownish fibrous
crystal groupings of Sillimanite have come from Chester, Middlesex Co., Connecticut. Also in Connecticut are the old classic locality of Norwich, New London Co.; and Willimantic, Windham Co., where small crystals in matrix
were found. Fibrous masses of Sillimanite come from Brandywine Springs, New Castle Co., Delaware; and dark brown crystals crystal sprays from Oconee Co., South Carolina. Gray Sillimanite masses are found in Natrona Co., Wyoming.