THE MINERAL SERPENTINE

  • Chemistry: (Mg,Fe)3Si2O5(OH)4, Magnesium Iron Silicate Hydroxide
  • Class: Silicates
  • Subclass: phyllosilicates
  • Group: Kalolinite-Serpentine
  • Uses: many industrial applications, including brake linings and fireproof fabrics and as an ornamental stone.
  • Specimens

Serpentine is a major rock forming mineral and is found as a constituent in many metamorphic and weather igneous rocks. It often colors many of these rocks to a green color and most rocks that have a green color probably have serpentine in some amount.

Serpentine is actually a general name applied to several members of a polymorphic group. These minerals have essentially the same chemistry but different structures. The following is a list of these minerals, their formulas and symmetry class:

  • Antigorite; (Mg,Fe)3Si2O5(OH)4; monoclinic.
  • Clinochrysotile; Mg3Si2O5(OH)4; monoclinic.
  • Lizardite; Mg3Si2O5(OH)4; trigonal and hexagonal.
  • Orthochrysotile; Mg3Si2O5(OH)4; orthorhombic.
  • Parachrysotile; (Mg,Fe)3Si2O5(OH)4; orthorhombic.
Their differences are minor and almost indistinguishable in hand samples. However, the chrysotile minerals are more likely to form serpentine asbestos, while antigorite and lizardite form cryptocrystalline masses sometimes with a lamellar or micaceous character. Asbestos had been used for years as a fire retarding cloth and in brake linings. Its links to cancer however has led to the development of alternative materials for these purposes.

Serpentine's structure is composed of layers of silicate tetrahedrons linked into sheets. Between the silicate layers are layers of Mg(OH)2. These Mg(OH)2 layers are found in the mineral brucite and are called brucite layers. How the brucite layers stack with the silicate layers is the main reason for the multiple polymorphs. The stacking is not perfect and has the effect of bending the layers. In most serpentines, the silicate layers and brucite layers are more mixed and produced convoluted sheets. In the asbestos varieties the brucite layers and silicate layers bend into tubes that produce the fibers.

Serpentine can be an attractive green stone that takes a nice polish and is suitable for carving. It has been used as a substitute for jade and is sometimes difficult to distinguish from jade, a testament to the beauty of finer serpentine material.

Non-fiberous serpentine is not a cancer concern. Asbestos serpentines should be kept in closed clear containers, but makes an attractive specimen. Sometimes with a golden color as the name chrysotile in greek means golden fibers.

PHYSICAL CHARACTERISTICS:

  • Color is olive green, yellow or golden, brown, or black.
  • Luster is greasy, waxy or silky.
  • Transparency crystals are translucent and masses are opaque.
  • Crystal System is variable, see above.
  • Crystal Habits: never in large individual crystals, usually compact masses or fibrous. Veins of viberous serpentine can be found inside of massive serpentine or other rocks.
  • Cleavage the varieties of crysotile have none, in lizardite and antigorite it is good in one direction.
  • Fracture is conchoidal in antigorite and lizardite and splintery in the crysotiles.
  • Hardness is 3 - 4.5
  • Specific Gravity is 2.2 - 2.6
  • Streak white
  • Associated Minerals include chromite, olivine, garnets, calcite, biotite and talc.
  • Other Characteristics: serpentine in the rough has a silky feel to the touch and fibers are very flexible.
  • Notable Occurances Val Antigorio, Italy; Russia; Rhodesia Switzerland; North Carolina, California, Rhode Island and Arizona, USA and Quebec, Canada.
  • Best Field Indicators softness, color, silky feel and luster, asbestos if present and its flexibility.
SERPENTINE specimens:
(hover for more info)
SERPENTINE specimen ser-1
$ 60.00
Dims: 10-5/8" x 6-1/2" x 3-1/2"
Wt: 5 lbs,. 4 oz
unknown
This mineral is known as Chrysotile, a fibrous variety of the mineral Serpentine. This piece in particular is compact and fibrous, ranging in color from light to dark green. The fibers are difficult to separate from the mass, and though classified as an asbestos, this mineral poses no health hazards, as it is Tremolite Asbestos that is the more dangerous variety. This specimen is the type that is a very common mineral, but not very many collectors have a sample of. We hope to change that.
no photo
ser-1 ($ 60.00)
unknown
SERPENTINE specimen ser-2
$ 25.00
Dims: 4" x 1-7/8" x 1"
Wt: 2.6 oz
Chestnut Hill, Easton, Pennsylvania, U.S.A.
Not only have I never seen one of these specimens before, I never heard of such a transformation occurring! This specimen is a Serpentine pseudomorph after biotite; it's variety name is Eastonite, most likely named after Easton, the town in which this mineral was found. It looks a lot like a muscovite book, but is a little bit less "micaceous" looking, and looking at the sides perpendicular to its basal faces, some parts of it look definitely like serpentine. Bizarre!
no photo
ser-2 ($ 25.00)
Chestnut Hill, Easton, Pennsylvania, U.S.A.
SERPENTINE specimen ser-3
$ 45.00
Dims: 5.0 x 3.1 x 2.1" (12.6 x 7.8 x 5.4 cm)
Wt: 1 lb., 7.5 oz. (665 g)
Gila County, Arizona, U.S.A.
This display-size specimen consists entirely of Serpentine, in alternating massive and compact, fibrous layers. All have a dull green coloration; the massive and fibrous materials have corresponding dull and pearly lusters, respectively. No actual crystals are visible, and other than a spot of damage on one side, the piece is in excellent condition.
no photo
ser-3 ($ 45.00)
Gila County, Arizona, U.S.A.
SERPENTINE specimen ser-4
$ 25.00
Dims:5.2x3.1x1.4" (13.2x7.9x3.6 cm)
Wt: 14.7oz. (418g)
Thetford, Quebec, Canada
This is a specimen of the mineral serpentine, variety chrysotile. It is extremely fibrous in nature. The reflection of light from the face of this specimen is quite pleasing. In fact, when chrysotile is pseudomorphed by quartz, it is known as the popular "tiger eye". There is no noticable damage to this specimen. Chrysotile fibers are the closest thing to actual crystals that serpentine ever achieves.
no photo
ser-4 ($ 25.00)
Thetford, Quebec, Canada

 


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