SFMOMA has acquired an unusual piece of postwar minimalist art by Sol LeWitt, the museum announced today. The work is called Wall Grid (3 x 3); it was produced in 1966. It's one of LeWitt's "structures," three-dimensional works in steel or wood that characterized his output from 1964 to 1968. Museum curator Gary Garrels says Wall Grid (3 x 3) is a rare type of work, explaining that minimalist artists created pieces with this kind of ultra-simplicity only from 1964 to 1966 or 1967. Minimalist artists in this period aimed "to take art to its most fundamental basic existence," Garrels says, by removing as much as possible from their pieces while still preserving an aesthetic of beauty. SFMOMA has other works by LeWitt from the early 1970s, Garrels said, but "this kind of really reductive, bare-bones piece has been missing for us." "It has, I think, an incredible visual presence," he adds. "It's the perfect example of LeWitt." The acquisition of Wall Grid (3 x 3) brings the number of LeWitt pieces in SFMOMA's holdings to 73 -- one of the largest LeWitt collections in the world, according to the museum. The museum would not release the amount it paid for the piece, but similar wooden wall structures by LeWitt have sold at auction for $14,000 to more than $200,000, according to FindArtInfo.com. Garrells said the museum is doing some conservation work on the piece and hopes to begin displaying it in the next few months.