Almost 35 years ago McCoy Tyner made his big-league jazz debut in a short-lived band known as the Jazztet. That band was led by Art Farmer and Benny Golson, each of them an important and compelling artist; nonetheless it is Tyner who has established himself as the most influential member of that group, and among the most dynamic and original stylists in the history of jazz piano. Once you've heard him, you don't mistake anyone else for him--except for the scores of younger artists who have built their own styles on his (or amalgamated it with those of Chick Corea, Herbie Hancock, or Keith Jarrett). By the time he left John Coltrane's juggernaut of a quartet in 1965, Tyner had nurtured the denser thickets of Bud Powell's keyboard style into a burgeoning forest of dark textures, percussive accents, and sharply angled melodies. But by the 1980s he had learned to let some light in. His tempos, his voicings, and even the arc of his improvised lines took on a welcome buoyancy; subsequently he began to tread the territory of the gracefully maturing jazz musician, reinvestigating classic tunes and standard formats (such as the big band with which he last played Chicago) while continuing to write and perform his own pulsing, elemental compositions. Does Tyner's undeniably brilliant, even unique approach to the piano constitute genius? On the one hand that term gets thrown around a lot; on the other, we usually have trouble spotting the real thing during his or her lifetime. At any rate Tyner, in his mid-50s, has crossed that awkward stage in which a musician's relative youth belies the weight of his career. To celebrate, he keeps spinning skeins of high-carat gold on a regular basis. Friday through Sunday, Joe Segal's Jazz Showcase, Blackstone Hotel, 636 S. Michigan; 427-4846.