Table 7.8.

Field terms for description of consistency in soils and strength in rocks

Term for field useField estimate of soil consistencyTerm for field useField estimate of rock strength
Extremely softFinger pushed in easily to full extent; unable to maintain shapeExtremely weakScratched by thumbnail; gravel-sized lumps crush between finger and thumb
Very softFinger pushed in up to 25 mm; exudes between fingersVery weakGravel-sized lumps can be broken in half by heavy hand pressure; crumbles under firm blows with point of a geological hammer; can be peeled by a pocket knife
SoftFinger pushed in up to 10 mm; moulds by light finger pressureWeakCan be peeled with a pocket knife with difficulty; shallow indentation made by firm blow with point of a geological hammer; rock broken by hammer blows when sample held in hand; thin slabs, corners or edges can be broken off with heavy hand pressure
FirmThumb makes impression easily; cannot be moulded by fingers; rolls to threadMedium strongCannot be scraped or peeled with a pocket knife; specimen resting on a solid surface can be fractured with a single blow from a geological hammer
StiffIndented slightly by thumb; crumbles, breaks; remoulds to lumpStrongSpecimen resting on a solid surface requires more than one blow of a geological hammer to fracture it
Very stiffIndented by thumbnail; crumbles, does not remouldVery strongSpecimen requires many blows of a geological hammer to fracture it; specimen chipped by hammer blows
Extremely strongSpecimen can only be chipped with a geological hammer; can only be broken by sledge hammer; rings on hammer blows