[ JO ] PRISMATIC HEAVY SPAR. Fig. j i i. Oblique, four-fided prifm, bevilled on both extremities, thebevilling planes let on the acute lateral edges. CELESTINE. Fig. 12 2. Oblique four-fided prifm,- bevilled on both extremities, the bevilling planes fet on the acute lateral edges. Fig. 122- Preceding figure', truncated on the lateral edges. Fig. 133. Oblique four-fided prifni, acuminated by four planes, which are fet on the lateral edges, and the acuminating planes ending in a line. Fig. 124. Six-fided table. plate rr. In giving an account of the cryftallizations of a mineral, we mention its fundamental figure or fi gures, deferibe their varieties, and arrange them ac* cording to their natural alliances. Colour, which is a very important character, mult alfo be treated in a fimilar manner; the fpecies and varieties mftft be corre&ly determined, and arranged according to theif affinities with each other, otherwife, particularly in minerals pofieffing extenfive fuites of colour, as dia mond and fapphire, ir would be very difficult to re collect them, and when remembered would not con vey to the mind a very diftinct picture of this highl/ interefting character. I have, therefore, been careful in the deicriptions to determine the colours with prc- cifion, and to arrange them as much as poffible in a natural order. In the trearife of Hauy, the colours are not arranged, and very feldcm accurately deter mined \ this is the cafe, although not in fo great i degree, with a more uleful work, the Mineralogy of Brochant. Id