Diamond shaped objects in the sky, in triangular

3diamond shaped object, flying in precise triangular formation at high elevation traveling SW at high rate of speed. These objects did not look like normal jet aircraft. The objects were in extremely tight formation. These objects appeard to be black in color. At the altitude that they were flying, I would think that the color would not be visible, in either color or formation. The whole sighting lasted 5 seconds, from visibility until they were gone. I heard absolutely no sound.