Phyromorphite Composition,
Crystallization & Structure

Composition. Pb₄(PbCl)(PO₄)3 = Phosphorus pentoxite 15.7, lead protoxide 82.2, choclorine 2.6 the phospphorus is often replaced by arsenic and the species graduates into mimetite.

Crystallization. Hexagonal, tri- pyramidal. Prismatic crystals with basal plane. Rarely shows pyramid truncations. Often in rounded barrel-shaped forms. Some times cavernous, the crystals being hollow prisms (Fig. 350). Frequently in parallel groups

Structure. Crystals, globular, reniform, fibrous and granular.

Physical Properties. H. = 3.5-4. G. = 6.5-7.1. resinous luster. Color usually various shades of green, brown, yellow; more rarely orange-yellow, gray, white. Subtransparent to nearly opaque.

Test. Easil fusible (2). Gives a lead globule when fused on characoal with sodium carbonate. When fused alone on charcoal gives a globule which on cooling shows crystalline structure. Faind white sublimate of lead chloride whn heated in C. T. A few drops of the nitric acid solution added to ammonium molybdate slolution gives a yellow precipate of ammonium phosphomolybdate.

Occurrence. A mineral formed by secondary action and found in the upper oxidized portions of lead veins, associated with other lead minerals. Notable localities for its occurrence are the lead mines of Poullaouen and Huelgoat, Britany ; at Ems in Nassau; at Zchopau, Saxony; pribram, bohmia; Beresousk, Ural Mts.; in Cumberland and at Leadhills, Scotland; Phoenixville, Pennsylvania; Davidson County, North Carolina; from Idaho, etc.

Name. Derived from two Greek words meaning fire and form in allusion to the crystalline form it assumes on cooling from fusion.

Use. A subordinate ore of lead.