Mexican apatite refers principally to the yellow to yellow-green fluorapatite that comes from the Cerro del Mercado iron mine and other localities in the state of Durango. The Durango material has long been the global reference for collector apatite, and specimens from the deposit appear in mineralogical museums around the world. The mine is primarily a magnetite operation and the apatite is a by-product, occurring as well-formed hexagonal prisms in pegmatitic pockets within the iron-rich body.

The species is fluorapatite, a calcium phosphate with formula approximately Ca5(PO4)3F. Refractive index sits between 1.63 and 1.64, specific gravity near 3.18, and hardness is five on the Mohs scale, which is the practical limit for daily-wear jewellery and the reason the stone tends to be set in pendants and earrings rather than rings. Cleavage is poor and there is no sensitivity to ordinary household exposure, but the material is brittle and should be cut with care.

The signature Durango colour is a saturated golden yellow with a slight greenish modifier, often clean, and frequently faceted as bright cushions and rounds in the five to twenty carat range. Larger clean stones above thirty carats are uncommon. Mexican apatite is also found in colourless and pale green varieties, the latter sometimes confused with peridot at first glance but easily separated by refractive index and birefringence. The chatoyant and asterated cabochons known elsewhere in the apatite trade are not a Durango speciality.

Heat treatment is occasionally applied to deepen colour, although the Durango stones are sold most often as untreated. Disclosure is limited compared with the corundum trade. The material is stable to light and to brief immersion, but ultrasonic and steam cleaning are not advisable due to brittleness and the possibility of fluid inclusions.

For the working jeweller, Mexican apatite occupies a particular niche: a clean, highly transparent yellow stone with a refractive index close to topaz, useful when a citrine looks too pale and a yellow sapphire is out of budget. Provenance to Durango is a recognised premium when pieces can be matched to documented mine output.