194 BULLETIN 118, UNITED STATES NATIONAL MUSEUM. 



Plasma=massive translucent quartz, dark grass-green in color, sometimes with white 



or yellow inclusions of celadonite or of delessite. 

 Pleonaste= black spinel. 



Polycrase=black mineral similar in composition to euxenite. 

 Porcelain jasper=a Daturally indurated clay. 

 Porphyry=rock, variegated in structure, with individual crystals much larger than 



the fine-grained matrix. 

 Potstone=soapstone (impure talc). 

 Prase =massive, translucent, and spotted quartz of a green to leek-green color caused 



by inclusions of minute crystals of actinolite or other minerals. 

 Prase opal=apple-green translucent opal. 

 Precious coral =red coral. 

 Precious opal = opal showing a play of colors. 

 Precious schorl = tourmaline. 



Prehnite=greenish aluminum and calcium hydrous silicate. 



Prismatic moonstone = clouded chalcedony (quartz) from Mohave Desert, California. 

 Prismatic quartz=cordierite. 



Prosopite=aluminum and calcium hydrous fluoride. 

 Pseudochrysolite=moldavite. 

 Pseudodiamond= quartz crystal. 

 Pseudoemerald = malachite. 

 Pyrite=iron sulphide in isometric crystals. 

 Pyrope=blood-red garnet, aluminum and magnesium silicate. 

 Pyroxene=group of complex silicates of aluminum, iron, calcium, magnesium, and 



other elements. 



Q. 

 Quartz=crystallized silica. 

 Quebec diamond = quartz crystal. 

 Quinzite=rose-colored common opal. 



R. 



Radio opal=opal of a smoky color caused by organic inclusions or impurities. 

 Radiumite=mixture of black pitchblende, yellow uranotile, and orange gummite. 

 Rainbow agate=agate which shows iridescence when cut across the concentric 



structure. 

 Rainbow quartz =iridescent quartz. 

 Rattle boxes=limonite geodes. 

 Realgar=orange arsenic sulphide. 

 Reconstructed gem=one artificially made by fusing and recrystallizing fragments of 



natural gems. 

 Red stone=ruby. 



Resin opal=opal with a resinous luster. 

 Rhinestone = rock crystal (quartz). 

 Rhodochrosite=pink manganese carbonate. 

 Rhodolite=rose-colored garnet, between pyrope and almandite; aluminum, iron, and 



magnesium silicate; from Macon County, North Carolina. 

 Rhodonite=pink manganese silicate. 

 Riband agate=agate with parallel layers. 



Riband jasper=jasper with differently colored alternating bands. 

 Ribbon agate=banded agate. 



Ring agate=agate with differently colored bands arranged in concentric circles. 

 Ripe diamond =true diamond (see unripe diamond). 

 River agate = moss-agate pebbles found in brooks and streams. 

 River sapphire=light-colored sapphire from Montana. 





