"Beautiful" is one of the most overworked adjectives in the English language, but when the subject is Joni Mitchell - her music, her voice, her person - it is the only one that fits.

At a recent concert, Joni was into the third tune and her touring band, the L.A. Express, was chugging. She stepped up to the microphone, but someone in the audience called out to turn the volume down.

Joni cocked her head and gave him a wry grin.

"Oh, boy," she said. "We've got a house full of purists. Can you hear the words?"

Yes.

"Well, all right then."

If Joni Mitchell was ever a "folk singer," she is no longer. She is a unique musical entity and her music refuses to be forced into any such die-cut molds.

She is one of only three or four current songwriters deserving of the title "genius." Hers is a brilliantly personal kind of music - intensely and revealingly intimate.

But unlike some writers who attempt to lay bare their soul on the assumption that any bare soul should be of interest, Joni Mitchell serves herself up with a kind of joy that frees the listener from the uncomfortable feeling of prying into another's privacy.

Her new album, "Court and Spark" (Asylum 7E-1001), is very nearly perfect, representing both a consolidation of all that was best in her previous work while expanding the range of her personal idiom. The arrangements are bigger, the tempos and rhythms more varied; the big-name backing musicians (from Jose Feliciano and David Crosby to Cheech and Chong) superb. And Joni's voice - stunning in its range and emotional content.

The apparent delicacy of her music - even the straight rock tunes - is misleading. It comes from the way she forces too many words into each line, from her complex melodies, from her unique voice and delivery.

In reality, like some intricate Oriental construction, Joni Mitchell's music has a strength derived from the opposing tensions and stresses she places on it. That also explains why few of her songs are recorded by others: they depend on her personal delivery to become complete works. Beautiful.