The serpentine Mineral Group
Serpentine is not a single mineral, but rather a group of related minerals. Besides for the main members of Antigorite and Chrysotile, a distinction is not usually made between the individual members except under scientific study and classification. Antigorite usually represents the more solid forms, and Chrysotile usually represents the fibrous forms, especially asbestos. Chrysotile is further sub-classified into four member minerals by its crystallization, and Clinochrysotile is by far the most prevalent form of Chrysotile.
Fibrous Chrysotile, a type of asbestos, should never be brought near the mouth. If its fibers or particles enter the lungs, they can cause asbestosis. Asbestosis is a lung disease caused by inhalation of asbestos particles, which causes several cancers, particularly lung cancer and mesothelioma. Symptoms of asbestosis do not arise until about 20 years after the inhalation. Due to the hazards, washing hands after handling specimens is highly recommended. Many mineral collectors avoid collecting asbestos minerals out of safety concerns.
The Serpentine group is composed of several related minerals. A generic formula that includes all members is:
Where X = Mg, Fe2+, Fe3+,
Ni , Al, Zn, or Mn.
(One of the two Si atoms may also be replaced by an Al or Fe atom in a few rare members.)
This leads to a complete formula of (Mg,Fe,Ni,Al,Zn,Mn)2-3(Si,Al,Fe)2O5(OH)4.
(The subscripted 2-3 after the first set of elements denotes that there are two or three of the selected elements, depending on the charge of the element. Some very rare forms of Serpentine contain water [H2O] in place of the hydroxyl [OH]. Since the charge of water is different from hydroxyl, the formula of these rare forms is slightly altered.)
The two most common members of the Serpentine Group are:
Antigorite - (Mg,Fe)3Si2O5(OH)4
Chrysotile - Mg3Si2O5(OH)4
Chrysotile is not a single mineral, but a group of polymorphous minerals with the same chemical composition but different crystal lattice. Chrysotile polytypes are:
Other members of the Serpentine group are:
Amesite - Mg2Al(SiAl)O5(OH)4
Cronstedtite - Fe2+2Fe3+(SiFe3+)O5(OH)4
Fraipontite - (Zn,Al)3(Si,Al)2O5(OH)4
Nepouite - Ni3Si2O5(OH)4
There are several additional members of the Serpentine group not discussed here due to there extreme rarity.
White, yellow, green, gray, brown, black, purple; sometimes multicolored, especially green and yellow.
Antigorite, Clinochrysotile, Cronstedtite, Fraipontite, and Nepouite all crystallize in the monoclinic crystal system.
Orthochrysotile and Parachrysotile crystallize in the orthorhombic crystal system.
Lizardite crystallizes in the hexagonal crystal system.
Amesite crystallizes in the triclinic crystal system.
Serpentine aggregates include massive, platy, fibrous (forming tough, flexible and elastic fibers), botryoidal, columnar, earthy, platy, micaceous, in pyramidal groupings, in parallel bladed groups, and as fibrous veins. Fibrous veins may be straight, but are more often in curved, angled veins. Some fibrous forms are extremely soft and flexible and resemble wool. Serpentine also pseudomorphs after many minerals, where it form in the same crystal shape as the pseudomorphed mineral.
Basic silicate of magnesium, iron, aluminum, nickel, zinc, and manganese. (Some rare varieties contain water in place of the hydroxyl, and substitute a different metal in exchange of the charge difference.)
Greasy feel, soft compared to similar minerals, and may flexible and elastic.
Serpentine is fairly common in many environments, and is an important rock forming mineral in many metamorphic environments.
Form of Serpentine that is massive shaped with densely packed fibers. It is usually greenish in color and is occasionally used as an ornamental stone.
Name describing a small group of green Serpentine minerals rich in nickel. It is also used as definition for a rock containing nickel-rich Serpentine, associated with Talc, Chllorite, and other soft minerals. May also be used a synonym for Nepouite.
Verde Antique is dark green rock composed of Serpentine, and often containing Calcite veins running through it. It is used as a decorative stone, and is sometimes wrongly considered a marble.
The finely fibrous variety of Chrysotile is the primary source for industrial asbestos. It produces approximately 95% of all asbestos (the other 5% is amphibole asbestos, such as Tremolite and Actinolite). Because it is not affected by fire and is a poor heat conductor, it is used for fire retardant devices and heat protection. Its former use, which has been outlawed in most areas, was as an insulator, but has been banned because of its notorious nature of causing cancer and other long term illnesses.
Antigorite, as well as Serpentinite and Verd Antique, are sculpted into ornamental carvings. They are soft and easy to work with, and create exceptional art. They are used as animal carvings, book ends, and the like. Verd Antique is also used as an ornamental green marble replacement, and is used as countertops, sculptures, plaques, and tiling. The varieties Deweylite and Williamsite are occasionally used
as minor gemstones, being polished as cabochons or beads. The
gemstone color is green or yellow green, and is usually mottled.
Serpentine gemstones resemble Jade, but are softer and inexpensive.
Serpentine is a very common mineral, and is found in abundance worldwide. Some famous localities include The Lizard Peninsula, Cornwall, England (the type locality of Lizardite; the Antigorio Valley, Piedmont, Italy (the type locality of Antigorite); and Mount Olympus, Cyprus. The Jeffery Asbestos Mine in Richmond Co., Quebec, is the one of the most productive asbestos mines, providing great amounts of Chrysotile. Thetford, in Megantic Co., Quebec has also produced fine Chrysotile.
In the U.S., large amounts of Serpentine come from Fresno, Calaveras, San Benito, Mariposa, and Toulumne Cos., California;
and Gila Co., Arizona. East Coast localities include Montville, Morris Co., New Jersey; Hoboken, Hudson Co., New Jersey; Antwerp, Gouverneur, and Balmat; St. Lawrence Co., New York; and Staten
Island (Richmond Co.), New York. In the old Tilly Foster Mine, Brewster, Putnam Co., New York, many minerals were replaced by Serpentine, resulting in the Serpentine having very interesting crystal forms.
The Wood's Chrome Mine in Texas, Lancaster County, Pennsylvania is a classic mine famous for both its Williamsite and a rare purple form of Antigorite that came from there. Other important occurrences are the Cedar Hill Quarry, Lancaster Co., Pennsylvania (especially the Picrolite variety); Easton, Northampton Co., Pennsylvania; and the Belvidere Mountain Quarries (Eden Mills), Orleans/Lamoille Counties, Vermont.
Below is a locality list for individual Serpentine members:
Amesite is found in Chester, Hampden Co., Massachussetts. It also occurs in Dufek massif, in the Pensacola Mountains, Antarctica; and is especially noted in Sarany in the Ural Mountains, Russia, for a rare purple variety. Cronstedtite is found in Salsigne, France; the Brunita Mine, La Union, Spain; Pribam, Bohemia, Czech Republic; and the Herja Mine, Baia Mare, Romania. It also occurs in Wheal Maudin and Wheal Jane, Cornwall, England; Congonhas de Campo, Minas Gerais, Brazil; and in Llallagua, Bolivia. Fraipontite is found in Challacollo, Chile; Vielle-Montague, Belgium and in the Silver Bell mine, Gleeson, Cochise Co., Arizona. It is often an alteration product of Smithsonite. Nepouite is found in the Nepoui Mine in New Caledonia. It is also found in the 132 North nickel mine, Widgiemooltha, Western Australia; in Letovice, Czech Republic; in Callenberg, Saxony, Germany; and in the Wood's Chrome Mine, Texas, Lancaster County, Pennsylvania. Nepouite is an important ore of nickel. It is often called Garnierite, but that is not its proper scientific name.
Distingushing Similar Minerals
Talc - Softer (1).
Chlorite - Softer (2 - 2½).
Tremolite and Actinolite Asbestos - Harder (5 - 6), less flexible.
Nephrite - Harder, less greasy.