When I saw this cacophony of color I knew I'd found my image of the week, but you'd never know it from reading the photo's caption alone. The simple caption of this Wellcome image reads, "crystals of urea."
Urea, also known as carbamide, is a waste product that's formed by humans - and other mammals, some fish and amphibians - when our bodies break down proteins. When we digest proteins, such as proteins in our food, it first forms a highly toxic compound, called ammonia. Fortunately, our bodies quickly convert ammonia to urea - a much less harmful waste product - and the urea is excreted from our bodies in urine.
Photo by Spike Walker/Wellcome Images