They're usually formed when breaking off from ice shelves; in this case, it likely came from the deteriorating Larsen C-the same shelf that saw a 2,200 square-mile, trillion-ton iceberg break away past year.
The spectacular photo of a massive rectangular iceberg with perfectly pointed edges, taken by a NASA research aircraft last week, left people scratching their heads as to how on earth this was possible.
And when they do break, it's usually geometrical in shape.
NASA scientists captured the image on an IceBridge flight, an airborne survey of polar ice.
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It studies yearly changes in thickness of sea ice, glaciers and ice sheets.
A triangular iceberg was also seen nearby, surrounded by several different types of sea ice. We get the type that everyone can envision in their head that sank the Titanic, and they look like prisms or triangles at the surface and you know they have a insane subsurface.
Such objects are not unknown, however, and even have a name - tabular icebergs.
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As the picture shows, tabular icebergs are large slabs of ice with almost vertical sides and flat tops.
NASA ice scientist Kelly Brunt said Tabular icebergs come about via a process "a bit like a fingernail growing too long and cracking off at the end".
"You can see at between 7-12 July 2018 the weather conditions and ocean currents conspire to swing the trillion tonnes of the giant iceberg A68 in an anticlockwise direction", he said.
"In the open water, grease ice is forming".
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"What makes this one a bit unusual is that it looks nearly like a square", she told the LiveScience website.