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.
*grə-no-, Proto-Indo-European root meaning "grain."
It is the hypothetical source of/evidence for its existence is provided by: Latin granum "seed," Old Church Slavonic zruno "grain," Lithuanian žirnis "pea," Old English corn.
in reference to granite strata in eastern Canada, 1854 (Sir W.E. Logan and T. Sterry Hunt), named for the Laurentian Mountains (where it is found), which are named for the nearby St. Lawrence River (see Laurence). Hence, Laurasia. The Laurentian library in Florence is named for Lorenzo (Latin Laurentius) de' Medici.
see set (n.1).
The extra t is an arbitrary addition in various technical senses, from a lawn-tennis to a granite set. Each class of persons has doubtless added it to distinguish the special sense that means most to it from all others ; but so many are the special senses that the distinction is now no more distinctive than an Esq. after a man's name, & all would do well to discard it. [Fowler]