[Illustration: Tourmaline crystals, growing amid feldspar crystals in a cavity in granite, from Paris, Me.] Plate 5 [Illustration: Gold in quartz, from California] Plate 6 [Illustration: Native silver in calcite] [Illustration: Argentite, the black masses throughout the white quartz] Plate 7 [Illustration: Pyrargyrite as it appears after moderate exposure to the light.] [Illustration: Crystal form of Pyrargyrite] [Illustration: Prousite as it appears after moderate exposure to the light] Plate 8 [Illustration: Native copper from Michigan] [Illustration: Chalcopyrite in tetrahedrons and an occasional octahedron.] Plate 9 [Illustration: Chalcocite crystals with the bluish tarnish] [Illustration: Tetrahedrite crystals] Plate 11 [Illustration: Cuprite, the red crystals showing characteristic color, other showing the green tarnish of malachite] [Illustration: Malachite (green) and azurite (blue), the two minerals shown together as they very commonly occur] Plate 12 [Illustration: Limonite] [Illustration: The crystal form in which goethite is found, _p_ is the prism faces, _b_ and _c_ are faces formed by beveling the edges of the prism, _o_ is the pyramidal face characteristic of the ends] Plate 13 [Illustration: Hematite, Clinton iron ore, oolitic] [Illustration: Siderite crystals] Plate 15 [Illustration: Pyrite crystals] [Illustration: Marcasite in concretionary form with radiate structure] Plate 17 [Illustration: Galena in crystals] [Illustration: Pyromorphite crystals (green)] Plate 19 [Illustration: Sphalerite, some the normal yellow and some crystals with the reddish tinge. (White is dolomite)] [Illustration: Zincite] Plate 21 [Illustration: Smithsonite in yellow crystals] [Illustration: Franklinite in octahedral crystals] Plate 24 [Illustration: Arsenopyrite, showing crystals massed so as to be incompletely developed] [Illustration: Realgar as it usually occurs in powdery incrustations] Plate 25 [Illustration: Large crystal of stibnite, the light colored face is the one parallel to which cleavage occurs] [Illustration: Niccolite as a vein in slate] Plate 26 [Illustration: Cobaltite, silver color, with pink tinge] [Illustration: Smaltite, pink is cobalt bloom] Plate 27 [Illustration: Carnotite from southwest Colorado] [Illustration: Cinnabar] Plate 31 [Illustration: Amethyst, not however deep enough colored for gems] [Illustration: Jasper, with botryoidal surface] Plate 32 [Illustration: Banded Agate from Brazil] Plate 33 [Illustration: Common Opal from Arizona] [Illustration: Siliceous sinter or Geyserite from The Yellowstone Park] Plate 35 [Illustration: A group of Microcline crystals from Pike’s Peak, Colo.]