Collection: Amphibole

Amphibole is a group of silicate minerals commonly found in igneous and metamorphic rocks. These minerals have a complex crystal structure and are characterized by the presence of double chains of silica (SiO₄) tetrahedra , which distinguishes them from other groups such as pyroxenes (which have single chains).

🔬 General characteristics

• General formula : $A_0-1B_2C_5T_8O_{22}(OH, F, Cl)_2$
  (where A, B, C, T represent different cations like Ca, Na, Mg, Fe, Al...)

• Crystal system : Monoclinic or orthorhombic

• Color : Green, brown, black, sometimes white (depending on the composition)

• Hardness (Mohs) : 5 to 6

• Luster : Vitreous to silky

• Cleavage : Good at 56° and 124°, typical of amphiboles

🧱 Examples of minerals from the amphibole group

• Hornblende : very common in igneous rocks (such as granites and diorites)

• Tremolite and actinolite : common in metamorphic rocks (schists, marbles)

• Anthophyllite : present in certain types of ultramafic rocks

• Glaucophane : indicator of high-pressure metamorphism (e.g., blue schists)

🧭 Formation and occurrence

Amphiboles are mainly formed:

• In water-rich igneous (plutonic or volcanic) rocks

• In metamorphic rocks resulting from the transformation of clayey or basic rocks, under high pressure and temperature

⚠️ Health and environment

Some fibrous varieties of amphiboles (such as tremolite or actinolite ) are part of amphibolic asbestos , a family of minerals that are hazardous to health. Inhaling their fibers can cause serious respiratory diseases such as asbestosis or mesothelioma .