Serpentine derives its name from the mottled appearance of its surface, which is supposed to resemble the skin of a serpent.
Pure serpentine is a hydrated silicate of magnesia, but it is generally found intermixed with carbonate of lime, with steatite or soapstone (also a silicate of magnesia), or with diallage, a foliated green variety of hornblende and dolomite.
Some varieties have a base of olive-green, with bands or blotches of rich brownish-red or bright-red, mixed with lighter tints, or olive-green, with steatite veins of greenish-blue; some are red, studded with crystals of green diallage; some clouded, and some striped.
Serpentine is massive or compact in texture, not brittle, easily worked, and capable of receiving a fine polish. It is so soft that it may be cut with a knife.
It is generally obtained in blocks from 2 to 3 feet long, and it has been found that "the size and solidity of the blocks increase with their depth from the surface."l
This stone is greatly used in superior buildings for decorative purposes. It is, however, adapted only for indoor work, as it does not weather well, especially in smoky atmospheres, for it is liable to attack by hydrochloric and sulphuric acids. The red varieties are said to weather better than those of a greenish hue, and it is stated that those varieties especially which contain white streaks are not fit for external work.
English. - Lizard Serpentine, from the Lizard promontory in Cornwall, is perhaps the best known and most extensively used in this country.
There are three varieties of this Serpentine to be found in the locality.
1. "The principal mass, like that of some other districts, is of a deep olive-green, but this is variegated by veins or bands and blotches of rich brownish-red or blood-red, mixed with lighter tints." l
"The best places for obtaining the red-striped varieties which we have seen, occur at the Balk near Landewednack, at the Signal Staff Hill near Cadgwith, at Kennack Cove, and on Goonhilly Downs."
2. "A variety, with an olive-green base, striped with greenish-blue steatite veins, is found . . . near Trelowarren." 2
3. "An especially beautiful variety is found at Maen Midgee, Kerith Sands, in which the deep reddish-brown base is studded with crystals of diallage, which, when cut through and polished, shine beautifully of a metallic green tint in the reddish base." 2
Greenish and reddish serpentines are found at Llanfechell and Ceryg-mollion; and a serpentinous marble at Tregola, near Llanfechell and near Holyhead.
Serpentine rocks occur in several localities in Scotland.
That of Portsoy, in Banffshire, "is very rich and varied in colour. It passes from soft green to deep red, and is variegated with veins of white steatite."
Serpentine is also found in the Ochil Hills, Aberdeenshire, at Killin in Perthshire, and in the Shetland Isles, where it forms the matrix of the chrome iron ore.
Connemara (Co. Galway) furnishes a serpentine in large blocks, commonly known as Connemara Marble or "Irish Green" marble. It is of two kinds.
The first is of a deep uniform shade of dark green, but the other is mottled, and made up of bands and stripes of greens of different shades, interlaced with white streaks.
The principal quarries are near Ballinahinch, Letter/rack, and Clifden.
Other green serpentines are found at Crohy Head, and Aughadovey in Donegal, and near Lough Gill in county Sligo.3
Vert Antique is a name applied to many varieties of green serpentinous rock used by the ancient Romans. "These ornamental stones, exported from the ruins of buried cities, have been recut and polished, and are now used in the internal decorations of modern buildings." 4 A detailed description of the different varieties will be found in Professor Hull's Treatise on the Building and Ornamental Stones of Great Britain and Foreign Countries.