What about https://simple.wikipedia.org/wiki/Diamond?
Compare with the Britannica one: 'diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.'
Britannica concisely summarizes the basic knowledge about diamonds in an easy-to-read short paragraph.
Wikipedia is uneven, some popular topics are well covered and have good info, others are outdated, biased, often written by one person with agenda.