- The predominant organic substance in the matrix of bone tissue is Collagen, specifically type I collagen.
- This protein forms a strong and flexible framework that provides tensile strength to the bone.
- The bone matrix is composed of both organic and inorganic components; while the inorganic part mainly consists of hydroxyapatite crystals, the organic matrix is primarily made up of collagen fibers that help resist stretching and twisting forces.

- Elastin is a protein found mostly in elastic tissues such as skin and blood vessels, giving them elasticity but it is not a major component of bone.
- Keratin is a structural protein found mainly in skin, hair, and nails.
- Chondroitin sulfate is a glycosaminoglycan present largely in cartilage, contributing to its resilience and hydration but not as a primary component of bone matrix.

Hence, the organic matrix of bone is predominantly collagen, which is critical for its structural integrity and mechanical properties.

Reference: Gray’s Anatomy, 41st Edition, Volume 1, Chapter 6 / Page 500