The Chennai police on Thursday arrested nine persons and recovered a stolen green stone valued at crores of rupees.

Joint Police Commissioner A Sailendra Babu said the uncut, green avin-surin quartz, weighing 52 kgs, could be centuries old and 'invaluable'.

He put the price at Rs 50 crore, and said that the help of archaeologists has been sought to fix the monetary value of the stone.

The stone belonged to one Krishnananth Swamiji in Ayyanapuram locality in the city. A nine-member gang, led by one Harinath, the brother of a retired judicial officer Kusumakumari who had joined the Swamiji's order, took away the quartz stone at knife-point on September 16.

Though the gang managed to saw away a part of the green stone, they could not market it because of the publicity on the theft, the police explained.