It’s curious to think that without a little rust, Uluru wouldn’t be red at all. This extraordinary rock formation rears abruptly from the heart of Australia’s dusty, russet desert and famously glows a fiery orange-red, especially at sunset. As you hike round the base of what’s probably the world’s largest monolith, think also about Uluru being made up of arkosic sandstone. This acquires its distinctive reddish hue when exposed to oxidation and the iron in the arkose rusts. So what color would this iconic, vivid chunk of rock be without a little chemical decay? A dismal, rather dull grey.