1832: Rain of Mud in Buenos Aires
According to author Charles Tomlinson, writing in 1864, a very odd 'rainfall' occurred in Buenos Aires, South America, decades earlier. As Tomlinson tells the story, in the early part of 1832 the climate of Buenos Aires had become unforgivingly dry, turning the entire region into the equivalent of a desert. Winds kicked up clouds of dust so dense that they occasionally blocked out the midday sun... and though the people fervently wished for rain, when the rain finally came things got much worse. The rain mingled with the heavy dust storms in the atmosphere, and large blobs of mud rained down instead of water. Houses looked as if they been puposely plastered with dirt; and the mud fall was so dense that many flocks of sheep were actually smothered by the fall.
Since the only source I've found for this account yet is in Tomlinson's book, The Rain-Fall and the Storm-Cloud, which was published just over thirty years after the mud-fall is said to have occurred, I've marked this account as unreliable until I can find evidence closer to the time of occurrence. Still a good story, though!