THE GLACIAL PERIOD 71 



if the fragmei- -,, c waterworn, as gravel, the result is a pudding 

 stone or conglomerate. The sand beds transform to sandstone 

 and clay to shale, readily known by the ease of its separa- 

 tion into flakes. The plant material transforms into peat and 

 coal. 



So soft they can 

 be scratched with 

 the fingernail 



Easily scratched 

 with a knife 



Chalk, 0.5-2.5 



Chlorite, 1.5-4.0 



Gypsum, 1.5-2.0 



Kaolin, 0.5-2.5 



Mica, 2.2-5.0 



Galenite, 2.5 



Serpentine, 2.5-4.0 



Calcite, 3 



White to gray, dull, crumbles in 

 fingers, no earthy odor when 

 breathed upon, effervesces with 

 acid. 



A green mineral of pearly to 

 vitreous luster with greasy feel- 

 ing. It usually occurs in grains 

 or scales in basic rocks. 



Many colors, streak always 

 white. Massive (alabastine), 

 fibrous (satin spar), foliated (if' 

 transparent called selenite). 



Many colors, streak like color. 

 Feels greasy. Strong clay odor 

 when breathed on. Dull to 

 pearly luster; brittle. 



Perfect cleavage; very thin 

 elastic scales can be obtained. 

 The black sort is biotite; the 

 colorless, gray, or pale green, 

 muscovite. 



Lead gray, streak same. Metal- 

 lic luster. Very heavy; cleaves 

 in cubes. 



Color, shades of green. Luster 

 greasy, waxy, or earthy. Feels 

 smooth or greasy. Compact and 

 amorphous, making a rock of 

 the same name. 



Many colors, streak white to 

 gray. Always cleaves into 

 rhombs. Effervesces in dilute 

 acid. 



