Each diamond over 0.30 carats is accompanied by a diamond-grading certificate from the Gemological Institute of America, or Antwerp-based Diamond High Council HRD, or the International Gemological Institute.

Source: https://www.ft.com/content/40bceee4-6c81-45f4-8bca-ce391b7be408

It's hard to say what the monetary value of the diamond is as, as well as carats, it depends on its cut, clarity, color.

Source: https://www.dailymail.co.uk/news/article-12887349/Arkansas-man-unearths-4-87-carat-diamond-visit-Crater-Diamonds-State-Park-10-minutes-mistaking-glass.html?ns_mchannel=rss&ns_campaign=1490&ito=1490

Other major sales from the same day included a rectangular modified brilliant-cut, fancy intense pink diamond of 8.77 carats selling for US$5,172,429 and a Burmese cushion-shaped ruby of 21.88 carats selling for US$2,611,280.

Source: https://www.samfordcrimson.com/bleu-royal-diamond-sold-for-44-million-at-christies-auction-in-geneva-switzerland-2023-11-12.html

Other major sales from the same day included a rectangular modified brilliant-cut, fancy intense pink diamond of 8.77 carats selling for US$5,172,429 and a Burmese cushion-shaped ruby of 21.88 carats selling for US$2,611,280.

Source: https://www.samfordcrimson.com/bleu-royal-diamond-sold-for-44-million-at-christies-auction-in-geneva-switzerland-2023-11-12.html