THE MINERALS OF IDAHO 179 



dony geodes weathered from Tertiary basalts in the area covered by 

 the Hailey quadrangle in Blaine County, especially on Pole Creek, a 

 tributary to Little Wood River and in Custer County in Low Hills, 

 near the Junction of the North Fork of Lost River with the main 

 stream. The amethysts are rare, most of the geodes containing 

 colorless crystals, and no deeply colored stones have been seen. 

 Occasionally clear quartz crystals have an interior phantom crystal 

 outline in pale amethyst. 



d. PSEUDOMORPHOUS QUARTZ 

 HACKLY QUARTZ 



Owyhee County .—The De Lamar, Web foot, Chautauqua, and other 

 veins in the same vicinity are all distinguished by the universal 

 presence of a laminated quartz which is clearly of pseudomorphic 

 origin. Occasionally there is some of the more massive flinty variety, 

 but the laminated variety prevails from the croppings of the Big 

 Reef and Garfield to the lowest level of the De Lamar mine. This 

 laminated quartz forms a cellular network of thin and straight 

 intersecting laminae of quartz. These meshes generally consist of 

 a narrow median line adjoined on both sides by quartz, projecting 

 as minute crystals on the surface of the laminae. The angles of 

 intersection of the latter do not appear to follow any certain law. 

 In some cases the outside of the laminae may be smooth and the 

 inside only covered by the projecting points of crystals (pi. 3, upper) ; 

 moreover the inside of these pseudomorphs is usually chambered by 

 thin laminae, coated by comb quartz on both sides. Under the micro- 

 scope these ores show intermingled coarser and finer quartz. The 

 coarser part shows grains from 0.1 to 0.2 mm. in diameter, which 

 have a decided tendency to crystal form though the influence of 

 other individuals has prevented its perfect development. With 

 higher magnifying power the fine grained material also dissolves into 

 similar quartz mosaic. Both are mixed, the finer aggregate forming 

 lamellar or triangular areas separated by coarser masses. Valencia- 

 nite in abundant and minute crystals of rhombic form was identified 

 without doubt in the quartz from the Chautauqua tunnel. It has 

 not yet been discovered in that from the De Lamar mine. 72 Such 

 hackly pseudomorphs have been found in precious metal veins in 

 other areas, particularly in the Jarbidge district, Nevada. The 

 structure seems quite certainly pseudomorphous after calcite of the 

 peculiar tabular habit, parallel to the basal pinacoid. A specimen 

 consisting of thick tabular plates of calcite making up a cellular 

 aggregate was collected by Lindgren from the Owyhee shaft. The 

 structure of this specimen is entirely analogous to that of some 



» Waldemar Lindgren. U. S. Qeol. Survey, 20th Ann. Rept., pt. 3, p. 170. 



