THE MINERALS OF IDAHO 203 



which were embedded in a mixed ocher of limonite and plattnerite 

 also containing scattering crystals of pyromorphite. A freshly 

 broken surface of the compact nodules shows a small conchoidal 

 fracture and a metallic-adamantine luster which tarnishes and be- 

 comes dull on exposure to the atmosphere for a few weeks. The 

 outside of the nodules is reddish brown (pi. 5, lower), while the 

 interior on fresh fracture is iron black with a compact cryptocrystal- 

 line structure. The streak is chestnut-brown; hardness 5.5; specific 

 gravity 8.56. Before the blowpipe on charcoal in the oxidizing 

 flame it decrepitates and fuses at 1 with boiling and spurting, yield- 

 ing a globule of lead, which, on further heating coats the coal yellow. 

 It is easily soluble in dilute hydrochloric acid, giving off chlorine. 

 An analysis by Yeates of a pure fragment yielded the following 

 results: 



Plattnerite, You Like lode 



Per cent. 



Lead 83. 20 



Silver Trace. 



Copper . 14 



Iron {}/2 aluminum) 1. 20 



Oxygen 13. 93 



Insoluble .82 



Total 99. 29 



Deducting impurities and recalculating to 100 per cent, this gives: 



Per cent. 



Lead 86. 55 



Oxygen 13. 45 



Total 100. 00 



Calcium and magnesium were present in appreciable amounts but 

 were not estimated. 



The individual nodules range from 2 by 1 by )4, to 8 by 6*4 by 434 

 inches, one of the largest of the original lot weighing 15 pounds, 4 

 ounces. Implanted upon many of them are the crystals of pyromor- 

 phite, which also speckle the interor. Some of these are brown from 

 thin coatings of plattnerite and look like crystals of that mineral. 

 Sometimes the plattnerite forms a cement binding together brecciated 

 fragments of vein quartz (pi. 5, upper). Some of the nodules 

 were found to be distinctly fibrous in part, fibers running from dense 

 cryptocrystalline material to small open cavities filled with bright 

 yellow ocher and terminating in minute jet black crystals projecting 

 into the ocher. These were too imperfect for the form to be made 

 out. Drusy sides of small fissures in some nodules were found to 

 contain measurable crystals. These were opaque, slender, and from 

 one-fiftieth to one one-thousandth of an inch long. They were 



