1640s, from French granit(e) (17c.) or directly from Italian granito "granite," originally "grained," past-participle adjective from granire "granulate, make grainy," from grano "grain," from Latin granum "grain" (from PIE root *gre-no- "grain"). In reference to the appearance of the rock. Used figuratively for "hardness" (of the heart, head, etc.) from 1839. New Hampshire, U.S., has been the Granite State at least since 1825.
-ic
Middle English -ik, -ick, word-forming element making adjectives, "having to do with, having the nature of, being, made of, caused by, similar to," from French -ique and directly from Latin -icus or from cognate Greek -ikos "in the manner of; pertaining to." From PIE adjective suffix *-(i)ko, which also yielded Slavic -isku, adjectival suffix indicating origin, the source of the -sky (Russian -skii) in many surnames. In chemistry, indicating a higher valence than names in -ous (first in benzoic, 1791).
In Middle English and after often spelled -ick, -ike, -ique. Variant forms in -ick (critick, ethick) were common in early Modern English and survived in English dictionaries into early 19c. This spelling was supported by Johnson but opposed by Webster, who prevailed.