Rock phosphate used in fertilizer manufacture is composed predominantly of which mineral species?

Introduction / Context:
Rock phosphate is the essential raw material for phosphatic fertilizers. Its mineralogy determines acid consumption, impurities, and downstream processing behavior. Recognizing the dominant mineral phase is basic to fertilizer technology.

Given Data / Assumptions:

• Typical sedimentary or igneous phosphate ores are processed.
• Industrial acidulation targets the apatite lattice.
• We select the principal mineral, not minor phases.

Concept / Approach:
Most rock phosphate deposits contain apatite-group minerals, especially fluorapatite with idealized composition Ca5(PO4)3F (often written Ca10(PO4)6F2 for the full unit). During acidulation (with sulphuric or phosphoric acid), the phosphate units are converted to water-soluble forms while fluorine may end up in by-products or emitted as HF unless scrubbed.

Step-by-Step Solution:
Identify common apatite: fluorapatite is prevalent in fertilizers-grade rock.Dicalcium and monocalcium phosphate are processed products, not major constituents of raw ore.Diammonium phosphate is a manufactured fertilizer, not a natural mineral in rock phosphate.

Verification / Alternative check:
Ore characterization studies for fertilizer plants routinely report fluorapatite as the main P-bearing phase, with varying carbonate substitution and accessory minerals (silica, clays, carbonates). Hydroxyapatite can occur but fluorapatite predominates in many deposits.

Why Other Options Are Wrong:
DCP and MCP form during processing; DAP is a finished product from ammonia and phosphoric acid; “hydroxyapatite only” is too restrictive.

Common Pitfalls:
Equating fertilizer product names with natural ore minerals; keep raw materials and manufactured products distinct.

Final Answer:
Fluorapatite