The AIM-listed firm said it believes that the 110 carat gem-quality light yellow diamond confirms the significant potential for larger stones that exists at the mine.
Stuart Brown, Firestone’s chief executive officer, said: "The 110 carat gem-quality light yellow diamond recovered during Liqhobong's ramp-up phase is a very exciting and encouraging accomplishment.
“It confirms our long held belief that Liqhobong has large stone potential and I hope this is the first of many to come."
In a note, Shore Capital analysts Yuen low said: The significance of this recovery lies in its confirming that the 75%-owned Liqhobong diamond mine in Lesotho has large stone potential.
“We echo the company’s hope that this will prove ‘the first of many to come’.”
In mid morning trading, Firestone shares were 8.4%, or 3.75p higher at 48.5p.
Panmure Gordon reiterated a ‘buy’ rating and 68p target price on Firestone.
In a note to clients, analyst Kieron Hodgson, said: “Given our knowledge of this operation and the diamonds we have seen previously, this reaffirms our long held belief that Liqhobong has the potential to produce these valuable diamonds.”
-- Updates share price, adds further broker comment --