Staurolite

Definition

Staurolite is a metamorphic mineral that typically appears as brown or reddish-brown crystals, often exhibiting a distinctive cross-shaped or cruciform pattern. It forms under medium-grade metamorphic conditions from the alteration of certain minerals like biotite and garnet, making it significant for understanding the processes and reactions that occur during metamorphism.

5 Must Know Facts For Your Next Test

1. Staurolite typically crystallizes in the orthorhombic system, which contributes to its characteristic cross-like appearance.
2. It is primarily formed in schists, a type of metamorphic rock, and is often associated with other minerals like garnet, kyanite, and biotite.
3. The presence of staurolite in metamorphic rocks can indicate specific pressure-temperature conditions during rock formation.
4. Staurolite has a relatively high specific gravity compared to other common minerals found in metamorphic rocks, which helps in identifying it in hand samples.
5. Due to its distinctive crystal habit, staurolite can also be used as an indicator mineral for geologists studying metamorphic environments.

Review Questions

• How does staurolite form during the metamorphic process, and what minerals does it commonly associate with?
  • Staurolite forms during medium-grade metamorphism when certain minerals such as biotite and garnet undergo changes due to heat and pressure. The reaction occurs under specific conditions that facilitate the growth of staurolite crystals, which often appear alongside other minerals like kyanite and garnet in schists. Understanding the formation of staurolite helps geologists decipher the metamorphic history of the rocks where it is found.
• Discuss the significance of staurolite's crystal structure and habit in relation to its identification in metamorphic rocks.
  • Staurolite's distinctive cross-shaped crystal structure is crucial for its identification among other metamorphic minerals. This unique habit arises from its orthorhombic crystal system, allowing geologists to recognize it quickly in fieldwork or laboratory studies. Its recognizable form not only aids in identification but also provides valuable information about the conditions under which it formed, enhancing our understanding of the metamorphic processes involved.
• Evaluate how staurolite contributes to our understanding of medium-grade metamorphism and what its presence reveals about geological conditions.
  • Staurolite serves as a key indicator of medium-grade metamorphism due to its specific formation conditions involving temperature and pressure. By studying where staurolite appears within metamorphic rocks, geologists can infer important details about the tectonic setting and thermal history of the area. Its presence often signifies particular environments where heat and pressure conditions were conducive to the growth of this mineral, thus providing insights into past geological events and processes that shaped the Earth's crust.

Related terms

Metamorphism:

The process by which existing rocks are transformed into new types of rocks through heat, pressure, and chemically active fluids.

Garnet: A group of silicate minerals commonly found in metamorphic rocks, known for their hardness and often used as gemstones.

Biotite: A common phyllosilicate mineral within the mica group, biotite is a major component of igneous and metamorphic rocks and plays a role in the formation of staurolite.