History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s3.t2.3

v1.c17.s3.t2.3

The family of beryl is a cyclosilicate Be₃Al₂Si₆O₁₈ which crystallises in the hexagonal system, sometimes occurring as long six-sided prisms, terminated by a basal plane (vide Kalidāsa’s long grass-green ratnaśalākā). In pure from, beryl is colourless. Lattice substitution by a very small quantity of chromium (in the form of Cr³⁺) makes the crystal light grass-green (typical vaidūrya of the early Sanskrit literature). Larger proportion of chromium (typically 0.2 per cent or above) results in intense green colour: ‘beautiful and deep emerald green to grass-green, unrivalled in depth and brilliancy and comparable to the fresh green of a meadow in spring’ (Bauer, 1968: 308).