The vein minerals, which are deposited in conduits for hot spring water, commonly possess attractive crystal forms; they include barite, quartz and amethyst, fluorite, calcite, datolite, galena, sphalerite, pyrite and others almost too numerous to list. Almost equally attractive crystals may be obtained from some metamorphic rocks, in which they have formed as heat and pressure abetted the growth of certain minerals at the expense of their less favored fellows; this group contains garnet, kyanite, chlorite, amphibole, epidote and many others. Less spectacular are the minerals resulting from the decay of rocks by percolating surface water, such as kaolin, limonite, some calcite, and the bright-colored copper carbonates. Two additional types of minerals are formed as the result of normal sedimentary and igneous processes, which will be described at length in connection with these two kinds of rocks. So, after the rock specimens are sorted from the minerals, the latter may profitably be arranged into five groups: 1. The Vein Minerals. 2. The Minerals of Pegmatites and Igneous Rocks. 3. The Minerals of Metamorphic Rocks. 4. The Minerals of Soils and Rock Decay. 5. The Minerals of Sedimentary Rocks. _The Vein Minerals_ The mineral list which follows is far from complete; it contains only those minerals which are most commonly found in casual visits to the localities discussed in connection with the local tours of the Connecticut Valley. Additional species are listed and described in any textbook on mineralogy. QUARTZ is a hard, white or colorless mineral which will scratch glass easily. In the technical language of the crystallographer, crystals are hexagonal or six-sided prisms, terminated by hexagonal pyramids; and the six flat faces which make the sides, together with the six triangular faces which form the apex, are readily recognized. Massive forms break with a curved or conchoidal fracture and were used by the Indians to make arrow-heads. The mineral is very abundant in all the lead veins and trap quarries; and in some of the latter, specimens of the purple variety of quartz, amethyst, are common. A black, smoky variety has been discovered in the pegmatite dikes of the highlands. Chemically quartz is the dioxide of silicon (SiO₂). CALCITE breaks along three smooth surfaces or cleavage planes. Each surface is rhomb-shaped, and the six rhombic faces fit together into a characteristic rhombohedral form. A knife will scratch the mineral easily. Calcite is abundant in the white veins of the trap quarries and is the principal constituent of the crystalline limestones in the Hoosac Valley between North Adams and Pittsfield. Calcite is a carbonate of lime (CaCO₃).