Biotite is an example of which type of rock-forming mineral?

Correct option is D

The correct answer is (D) Phyllosilicate

Explanation:
• Silicate minerals are classified based on the arrangement of the silicon-oxygen tetrahedron ($SiO_4$) units.
• Phyllosilicates (Sheet silicates) are minerals where the tetrahedra are linked in two-dimensional sheets. The word comes from the Greek 'phyllon' (leaf).
• Biotite (black mica) and Muscovite (white mica) are classic examples of phyllosilicates. They exhibit perfect cleavage, meaning they easily peel into thin, flexible sheets.
• Clay minerals (like Kaolinite and Montmorillonite) are also phyllosilicates, which explains their layered structure and expansion properties.

Information Booster:
• Biotite is a primary source of Potassium ($K$) and Magnesium ($Mg$) in soils upon weathering.
• It is a common constituent of igneous rocks like granite.
• Micas are used in electronics due to their excellent insulation properties.

Additional Knowledge:
• Orthosilicates (Option A): Individual $SiO_4$ units (e.g., Olivine).
• Inosilicates (Option B): Chain silicates; single chains (Pyroxenes) or double chains (Amphiboles/Hornblende).
• Tectosilicates (Option C): Three-dimensional framework silicates (e.g., Quartz, Feldspar).