1822) discovered brewsterite, Sr 2 (A14Si12032).10H20 , from Strontian, Scotland. He gave a set of interfacial angles for an orientation with the crystal's cleavage plane horizontal. Subsequent workers (Brooke and Miller, 1852; Greg and Lettsom, 1858; Mallet, 1859; Michel-Ldvy and Lacroix, 1888; Dana, 1892) depict brewsterite with vertical elongation and one can deduce from their measurements that the elongated vertical axis, c, is longer than the horizontal a-axis. Single crystal X-ray

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... ion studies (Strunz and Tennyson, 1956; Perrotta and Smith, 1964; Khomyakov et al., 1970) show it desirable to label the elongated axis as the a-axis to retain the standard space group setting for P2Jm. From these studies and the present work it is now certain that the X-ray orientation is c>a, elongation a, and it conflicts with the morphological orientation c>a, elongation c, because when the a and c axes reversed, in accordance with the X-ray results, the morphological orientation becomes c<a, elongation a. This confused state of affairs is reflected in two recent publications (Gottardi and Galli, 1985; Nawaz, 1988) which expose the conflicting orientations. The present note is written to clear the ambiguity surrounding the elongation question. [Manuscript