The sculpture, 7.5 metres high and weighing 2.7 tonnes, features an inverted obelisk with a broken shaft balancing on a pyramid in what the gallery's Senior Curator, International Art, Dr Lucina Ward, called "quite a feat of engineering and quite an exquisite work of art" .

It was one of four exemplars created and had previously been on display in Berlin. The first two sculptures are on display at the Rothko Chapel, Houston and the University of Washington's Red Square; the third exempler is in the open courtyard of the Museum of Modern Art in New York.

The gallery's director, Dr Gerard Vaughan, said "Broken Obelisk is one of the icons of Abstract Expressionism".

He said while viewers would find their own meanings in the work, to him it seemed to refer both to the classical tradition with its use of a pyramid and an obelisk (broken, referencing the damage done by the barbarians to the artworks of Greece and Rome) and in its inversion, to the modern era in which it was made.

"The '60s was the decade of revolution - it was conceived in 1963 and the first one was fashioned in 1966-67 ... and 1968 was the year of revolution around the world."

The work, he said, was "quietly subversive".

As well as being a significant artwork in its own right, he said, Broken Obelisk also heralded the forthcoming major American Masters 1940-1980 exhibition that will open on August 24.

One of the reasons the Barnett Newman Foundation lent Broken Obelisk to the gallery, he said, was "They realised we do have one of the best collections of 20th-century American art outside the United States".

Dr Ward said the American Masters exhibition will draw on the gallery's collection to focus on the New York school of artists such as Andy Warhol, Chuck Close, Louise Bourgeois and Eva Hesse .

Many of the works have not been exhibited for decades, if at all.

As for Pear – version number 2: Dr Ward said it will be relocated to the Australian Garden in the next three months.