A. Cannot be scratched easily with a knife; crystals or particles not
easily seen with the unaided eye; very hard, difficult to
break; may contain a few crystals or particles large enough to
see; granular
1) Dense; brittle; splintery or conchoidal fracture; sharp edges and
corners when broken; often associated with limestone; usually
white or gray; very dense, dull varieties called flint
Chert (27)
2) Light gray, pink, red, or tan varieties common; boulders or
fragments in the glacial drift
Felsite
3) Dark gray, greenish, black, or maroon varieties common; may have
small mineral-filled cavities; occurs as boulders or fragments
in the glacial drift
Basalt (4)
4) Essentially quartz; grains may be identifiable; specimens break
through rather than around grains
Quartzite (9)
B. May or may not be scratched with a knife; fairly uniformly fine
grained
1) Soft; feels slippery or soapy when wet; may disintegrate in
water; gives off an earthy odor when breathed upon
Clay
2) Loose; gritty; particles smaller than table salt
Silt
3) Solid rock; often in thin beds or sheets; separates into silt;
mica flakes may be present; may contain fossils; may effervesce
slightly
Siltstone
4) Solid rock; breaks into thin platy sheets; may feel slippery when
wet; black to gray; may contain fossils; shows thin laminations;
may effervesce
Shale (10)
5) Solid rock: does not break into thin platy fragments; may
effervesce slightly
Mudstone
6) Solid rock; usually gray or black; splits into platy sheets or
slabs; harder than shale
Slate
7) Powdery; white or light brown; commonly associated with chert and
quartz from which it forms
Tripoli (19)