what is a serpentin stone?

Question

what is a serpentin stone?

Answer 1

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.

Answer 2

Serpentine is a group of common rock-forming hydrous magnesium iron phyllosilicate ((Mg, Fe)3Si2O5(OH)4) minerals; it may contain minor amounts of other elements including chromium, manganese, cobalt and nickel. In mineralogy and gemology.

ck composed primarily of these minerals is called serpentinite. Serpentines find use in industry for a number of purposes, such as railway ballasts, building materials, and the asbestiform types find use as thermal and electrical insulation (chrysotile asbestos). The more attractive and durable varieties (all of antigorite) are termed "noble" or "precious" serpentine and are used extensively as gems and in ornamental carvings. Often dyed, they may imitate jade. Misleading synonyms for this material include "Korean jade", "Suzhou jade", "Styrian jade", and "New jade".

Answer 3

Serpentine is green and sometimes white, and occurs only in metamorphic rocks.

There are three main serpentine minerals:

- antigorite

- chrysotile

-lizardite.



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Answer 4

Serpentine is a group of common rock-forming hydrous magnesium iron phyllosilicate ((Mg, Fe)3Si2O5(OH)4) minerals; it may contain minor amounts of other elements including chromium, manganese, cobalt and nickel. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group. Owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine: antigorite, chrysotile and lizardite.



Overview

Serpentine is said to owe its name either to its serpent-like colours and patterns or from an old belief that the stones were effective protection from snake bites. They have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates. Alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the land surface, the soil is unusually high in clay.



Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures -- to over 600°C at depths of 60 km or so. In contrast, lizardite and chrysotile typically form near the Earth's surface and break down at relatively low temperatures, probably well below 400°C. It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs.



Samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight. Hence, antigorite may play an important role in the transport of water into the earth in subduction zones and in the subsequent release of water to create magmas in island arcs, and some of the water may be carried to yet greater depths.



Soils derived from serpentine are toxic to many plants, because of high levels of nickel, chromium, and cobalt; growth of many plants is also inhibited by low levels of potassium and phosphorus and low calcium/magnesium. The flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees (often conifers) within otherwise forested areas; these areas have been called "serpentine barrens".



Most serpentines are opaque to translucent, light (specific gravity between 2.2–2.9), soft (hardness 2.5–4), infusible and susceptible to acids. All are microcrystalline and massive in habit, never being found as single crystals. Lustre may be vitreous, greasy or silky. Colours range from white to grey, yellow to green, and brown to black, and are often splotchy or veined. Many are intergrown with other minerals, such as calcite and dolomite. Occurrence is worldwide; New Caledonia, Canada (Quebec), USA (northern California), Afghanistan, Cornwall, China, France, Norway and Italy are notable localities.



Rock composed primarily of these minerals is called serpentinite. Serpentines find use in industry for a number of purposes, such as railway ballasts, building materials, and the asbestiform types find use as thermal and electrical insulation (chrysotile asbestos). The more attractive and durable varieties (all of antigorite) are termed "noble" or "precious" serpentine and are used extensively as gems and in ornamental carvings. Often dyed, they may imitate jade. Misleading synonyms for this material include "Korean jade", "Suzhou jade", "Styrian jade", and "New jade". New Caledonian serpentine is particularly rich in nickel, and is the source of most of the world's nickel ore.



The Māori of New Zealand once carved beautiful objects from local serpentine, which they called tangiwai, meaning "tears". Material quarried in Afghanistan, known as sang-i-yashm, has been used for generations. It is easily carved, taking a good polish, and is said to have a pleasingly greasy feel.



The lapis atracius of the Romans, now known as verde antique or verde antico, is a serpentinite breccia popular as a decorative facing stone. In classical times it was mined at Casambala, Thessaly, Greece. Serpentinite marbles are also widely used: Green Connemara marble (or Irish green marble) from Connemara, Ireland (and many other sources), and red Rosso di Levanto marble from Italy. Use is limited to indoor settings as serpentinites do not weather well.



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