A pair of rare diamond and emerald spectacles from an unknown Indian princely treasury will be sold at an auction in London later this month.

The lenses were placed in the Mughal-era frames around 1890, according to auction house Sotheby's.

The spectacles will be offered at auction for £1.5m-2.5m ($2m-$3.4m) each, the auction house said.

Ahead of the sale, they will be exhibited in October for the first time in Hong Kong and London.

"These extraordinary curiosities bring together myriad threads - from the technical mastery of the cutter and the genius of craftsmanship to the vision of a patron who chose to fashion two pairs of glasses quite unlike anything ever seen before," Edward Gibbs, chairman of Sotheby's for Middle East and India, said.

It is unclear who commissioned these spectacles, but they possibly belong to Mughals, the dynasty that ruled the subcontinent in the 16th and 17th centuries and was known for rich artistic and architectural achievements.