RIO DE JANEIRO (AFP) - Rio's Christ the Redeemer statue, facing renovation after being struck by lightning last month, could take on a darker hue owing to a shortage of replacement stone, heritage officials said Sunday.

The 38-metre (including the pedestal) statue, named in a 2007 global poll as one of seven new wonders of the world, lost a fingertip to a lightning bolt during a January 22 storm.

But the repair work has prompted concerns over a much bigger overhaul planned for the 85th anniversary of the monument, which coincides with the 2016 Rio Olympics.

The city's Archdiocese wants to refurbish its soapstone mosaic outer shell - but that means finding six million small tiles of the same kind of stone.

And a survey of current supplies ahead of the fingertip repair suggests there might not be enough of the original quarry stone used in the 1931 construction.

Demand for the original stone, which comes from the southern state of Minas Gerais, is high in colder climates, where it is popular for fireplaces.

"These stones are extremely rare in that they have a clear verdant water hue, which nowadays is hard to find," said a spokesman for Brazil's national heritage institute Iphan.

"Remaining stone deposits are darker with a higher grade of talc, different from those used for the Christ (statue), which include other kinds of minerals and exceptional weather-resistant properties" Iphan explained.

Engineer-designer Heitor da Silva Costa selected the original stone for its resistance to extreme temperatures.

"We have sufficient stone for current restoration work - the concern is for later major work, such as for 2016," engineer Clezio Dutra told Rio daily O Dia.

The statue, created by Frenchman Paul Landowski, underwent a four-month US$4 million (S$5.1 million) restoration four years ago to fix cracks and water damage.

Some two million tourists a year head up Mount Corcovado through Tijuca Forest by tram, by car or on foot to enjoy an unbeatable view across Guanabara Bay.