Berlin, Königliche Akademie der Wissenschaften, 1837. 4to. 59 pp.; two large, folded engraved plates. Disbound. = Two papers on crystal systems, in particular in feldspars, published back-to-back, by the German mineralogist Christian Samuel Weiss (1780-1856). Published in the academy's Abhandlungen. "Weiss is credited for creating parameters of modern crystallography, and was instrumental in making it a branch of mathematical science. He stressed the significance of direction in crystals, considering crystallographic axes to be a possible basis for classification of crystals. He is credited for introducing the categorization schema of crystal systems, and has a basic law of crystallography named after him called the Weiss zone law"'.' (Wikipedia). Uncut. Plates a bit spotted, otherwise very good, unmarked.