18
stone
10
granite
9
rock
8
adamant
7
brick
6
iron
4
bone
4
cement
4
concrete
3
crystal(noun, hardness)
3
marble
3
quartz(noun, hardness)
2
firestone
2
heart of oak(expression, idiom, hardness)
2
flintstones
2
steel
1
pebble
1
Flint River(noun, expression, idiom)
1
crag(noun, hardness)
1
nail
<1234510>
11 years ago|5.3k views|share |citing 
APASmart Define. (2015). Flint thesaurus. Retrieved September 21, 2026, from https://smartdefine.org/flint/thesaurus/synonyms
ChicagoSmart Define. 2015. "Flint thesaurus" https://smartdefine.org/flint/thesaurus/synonyms (accessed September 21, 2026).
HarvardSmart Define 2015, Flint thesaurus, Smart Define, viewed 21 September, 2026, <https://smartdefine.org/flint/thesaurus/synonyms>.
MLASmart Define. "Flint thesaurus" 10 April 2015. Web. 21 September 2026. <https://smartdefine.org/flint/thesaurus/synonyms>