Because it cuts readily in all directions and takes a high polish, marble is widely used as a building stone. In the moist climate of the United States it suffers in being soluble in rain water when used on the outside of a building: but for interior decoration it furnishes some of the finest effects.
The largest marble quarries are developed in Vermont, Massachusetts, New York, Pennsylvania, Georgia, Alabama, Colorado, California, and Washington.
[Steatite]
Soapstone
Steatite is a rock composed essentially of talc, which is associated with more or less impurities, such as mica, tremolite, enstatite, quartz, magnetite, etc. It is found in and with metamorphic rocks, and is a rock which has been modified by hydration from a metamorphic predecessor. It was probably first a tremolite or enstatite schist, in which, after the metamorphic rock came into the zone where ground water exists, the tremolite or enstatite was altered to talc, the impurities remaining much as they were in the first place.
It is bluish-gray to green in color, often soft enough to cut with a knife, and has a greasy feel. It is very resistant to heat and acids; for which reasons it has proved very useful commercially in making hearthstones, laundry tubs, and fire backs; and, when powdered, in making certain lubricants. The Indians, in the days before Columbus, took advantage of the ease with which it is cut, to make from it large pots for holding liquids, which are today among the greatest treasures in collections of Indian relics. They also carved pipe-bowls and various ornaments and amulets from soapstone.
It is found in Vermont, Massachusetts, New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, Georgia and California.
[Serpentine]
[Pl. 67]
Pure serpentine is the hydrated silicate of magnesium, as described among the minerals on [page 138]. Serpentine rock is serpentine with more or less impurities, such as pyroxene, amphibole, olivine, magnetite, chromite, calcite, magnesite, etc. It often also contains mica and such garnets as pyrope, as accessory minerals. Serpentine, like steatite, always occurs in and with metamorphic rocks, and was originally a metamorphic rock, but has since been changed by the hydration of its silicates, when it came into the zone in which ground water is present. In the first instance it was some sort of shale, clay and dolomite, which was metamorphosed to an amphibole or pyroxene schist. When this was exposed to the action of ground water, the amphibole or pyroxene minerals were changed to serpentine, resulting in a rock composed mostly of serpentine, but retaining the impurities which were in the metamorphic rock, and perhaps adding to them such amphiboles and pyroxenes as were not altered during the hydration process. The above is the commonest type of serpentine rock. It can and sometimes has been formed in a similar way from an igneous predecessor, by the hydration of its silicate minerals. In this latter case the serpentine would not be a modified metamorphic rock, but a modified igneous one. It is a case where such a rock as a diorite or a gabbro is exposed to ground water and the pyroxene present altered to serpentine. A serpentine formed in this way would be a very impure one.
Serpentine rock is used as an ornamental stone for interior decoration, because it takes a high polish and has pleasing colors, various shades of green. It is however decidedly soft and will stand very little exposure to weather, and it is also filled with seams which make it difficult to get out large slabs.
Serpentine rock occurs fairly commonly in the metamorphic belt of New England and the Piedmont Plateau, and in some of the western states, especially California, Oregon, and Washington.