McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams

Home » Minerals » Staurolite

Staurolite


The metamorphic mineral that has become famous for its twinned crystals



What is Staurolite?



Staurolite is a mineral that is commonly found in metamorphic rocks such as schist and gneiss. It forms when shale is strongly altered by regional metamorphism. It is often found in association with almandine garnet, muscovite and kyanite - minerals that form under similar temperature and pressure conditions.


Properties of Staurolite



Staurolite is a silicate mineral with a generalized chemical composition of (Fe,Mg)2Al9Si4O23(OH). It is usually brown or black in color with a resinous to vitreous luster. It ranges from transparent to opaque in diaphaneity.

Staurolite is usually easy to identify when it occurs as visible grains in a metamorphic rock. Grains of staurolite are typically larger than the grains of other minerals in the rock and they often exhibit an obvious crystal structure. They occur as six-sided crystals, often with penetration twins.


Physical Properties of Staurolite

Chemical Classification silicate
Color usually brown, reddish brown, yellowish brown, brownish black, black, dark gray
Streak white to gray
Luster vitreous, sometimes resinous
Diaphaneity translucent to opaque, rarely transparent
Cleavage poor
Mohs Hardness 7 to 7.5
Specific Gravity 3.7 to 3.8
Diagnostic Properties color, six-sided crystals that are frequently twinned, usually found in schist and gneiss with muscovite mica and almandine garnet
Chemical Composition (Fe,Mg)2Al9Si4O23(OH)
Crystal System monoclinic
Uses


Twinning in Staurolite



The name "staurolite" is from the Greek word "stauros," which means "cross." The mineral commonly occurs as twinned, six-sided crystals that sometimes intersect at 90 degrees to form a cross. (An intersection angle of 60 degrees is more common.) In some localities these twinned crystals are collected, made into jewelry and sold under the name "fairy crosses."


Uses of Staurolite



There are very few uses for staurolite. It has been used as an abrasive, but that use has been replaced by other minerals and man-made materials. It is used in geologic field work to assess the temperature-pressure conditions of a rock's metamorphic history.

In locations where staurolite is found as well-formed cruciform twinned crystals it is sometimes collected, sold as a souvenir, made into jewelry, and used as an ornament. The cruciform crystals have often stirred religious beliefs and superstitions. Some of these objects are not staurolite, instead they are manufactured. If you see a selection of these for sale that are all the same size, the same shape and containing gas bubbles, they might be manufactured.

Staurolite is the official state mineral of the state of Georgia. It is especially abundant in a few localities in Patrick County. One of them is now "Fairy Stone State Park," named after the stone and the legends that surround it.


Contributor:


Mineral Information
 Anhydrite
 Apatite
 Arsenopyrite
 Augite
 Azurite

 Barite
 Bauxite
 Beryl
 Biotite
 Bornite

 Calcite
 Cassiterite
 Chalcocite
 Chalcopyrite
 Chlorite
 Chromite
 Chrysoberyl
 Cinnabar
 Clinozoisite
 Copper
 Cordierite
 Corundum
 Cuprite
 Diamond
 Diopside
 Dolomite

 Enstatite
 Epidote

 Fluorite

 Galena
 Garnet
 Glauconite
 Gold
 Graphite
 Gypsum

 Halite
 Hematite
 Hornblende

 Ilmenite

 Jadeite

 Kyanite
 Limonite

 Magnesite
 Magnetite
 Malachite
 Marcasite
 Molybdenite
 Monazite
 Muscovite

 Nepheline
 Nephrite

 Olivine
 Orthoclase

 Plagioclase
 Prehnite
 Pyrite
 Pyrophyllite
 Pyrrhotite

 Quartz

 Rhodochrosite
 Rhodonite
 Rutile
 Scapolite
 Serpentine
 Siderite
 Sillimanite
 Silver
 Sodalite
 Sphalerite
 Spinel
 Spodumene
 Staurolite
 Sulfur
 Sylvite

 Talc
 Titanite
 Topaz
 Tourmaline
 Turquoise

 Uraninite

 Witherite
 Wollastonite

 Zircon
 Zoisite


Find it on Geology.com




More from Geology.com


Diamonds from Coal
Biggest Misconception: Lots of people think that diamonds form from coal. Not True!
volcanic explosivity index
Volcanic Explosivity: Learn about some of the most explosive volcanic eruptions.
Plate Tectoncs
Zoom in on Plate Boundaries: See the details of plate tectonics in satellite view.
Fossils
Fossils: Learn about fossils and fossil discoveries around the world.
Rare Earth Elements
Rare Earth Elements are used in cell phones, DVDs, batteries, magnets & many other products.
Volcanoes
Volcanoes: Articles about volcanoes, volcanic hazards and eruptions past and present.
Sliding Rocks
Sliding Rocks Mystery: What causes these rocks to slide across a Death Valley playa?
Fluorescent Minerals
Fluorescent Minerals glow with spectacular colors under ultraviolet light.


Staurolite
Staurolite crystals forming the typical 60-degree penetration twin from Rubelita, Minas Gerais, Brazil. The specimen is about 1.5 inches tall. Photograph by Rob Lavinsky, iRocks.com. Used here under a Creative Commons License.




Staurolite
Twinned staurolite crystals in muscovite schist from Pestsovye Keivy, Keivy Mountains, Russia. This specimen of schist has one pair of staurolite crystals forming a 90 degree penetration twin (lower right) and another pair forming the more typical 60 degree penetration twin (upper left, partially embedded). Specimen is approximately 4 inches (10 centimeters) across. Photograph by Rob Lavinsky, iRocks.com. Used here under a Creative Commons License.


Staurolite
A specimen of quartzite with several brown staurolite crystals and blue crystals of kyanite. This specimen is about three inches wide and was collected in the Bernina Pass area, near Grischun, Switzerland. Photograph by Rob Lavinsky, iRocks.com. Used here under a Creative Commons License.


Staurolite
Staurolite in schist from Little Falls, Minnesota. Specimen is approximately 4 inches (10 centimeters) across.


Staurolite souvenirs
Staurolite crystals are often collected, made into jewelry and sold as souvenirs or "good luck" charms. Some of these items are genuine twinned staurolite crystals. Others are cross-shaped models manufactured for the tourist trade. If you see a selection of staurolite crosses offered for sale that are all the same size, same shape and have air bubbles on close examination they might be manufactured.


Diamonds Don't Form From Coal
East Africa Rift
World's Biggest Tsunami
What Causes a Tsunami?
Mount Rainier Volcanic Hazards
Rare Earth Elements
Teaching Plate Tectonics with Drawings
Largest Eruption of the 20th Century




© 2005-2014 Geology.com. All Rights Reserved.
Images, code and content of this website are property of Geology.com. Use without permission is prohibited. Pages on this site are protected by Copyscape.