This diamond was discovered in Botswana - the largest in a century. Photo: Monirul Bhuiyan / AFP
As the second-biggest diamond is dug out of the earth, science correspondent Allan Blackman looks at why we use the term carat to describe them and why they spontaneously turn into graphite.
He also details another study which found placebos - even when people knew they were taking a placebo - can have a positive effect on stress and depression.
And Queen's Brian May has quite the scientific background - a new BBC documentary follows his decade-long research to understand what's behind bovine TB and whether the continued culling of badgers is really the solution.
Allan Blackman is a Professor of Chemistry, School of Science, Auckland University of Technology.
