The Lost Songs of St Kilda sold out within a few hours of its release and has become the fastest-selling posthumous artist debut in history.
The album was recorded on a Â£3 microphone in an Edinburgh care home by pensioner Trevor Morrison.
The tracks have been reworked by a number of leading composers.
They include Sir James Macmillan, Craig Armstrong, Mercury Prize nominee Christopher Duncan, Rebecca Dale and Teenage Fanclub drummer Francis Macdonald.
To celebrate the release of the album, Sir James undertook the eight-hour boat journey to perform a special piano concert on the islands - the first time music had been heard on St Kilda since its evacuation in 1930.
It was also the first time a piano had ever been taken there. The instrument had to be dismantled for the journey, then reassembled.
Sir James said: "It has been a delight being involved in this project. Trevor Morrison's playing of the old St Kilda songs are genuinely poignant and haunting.
"He plays with a true musician's sensitivity, and communicates the beauty and simplicity of this lost music.
"It was marvellous that so many Scottish musicians and composers from different genres have responded to the originals with their own unique perspectives."
As a 10-year-old child on the west coast island of Bute during World War Two, Trevor had been taught piano by a former resident of St Kilda.
While living in a care home and suffering ill health, Trevor managed to remember the tunes his teacher had shown him.
And Stuart McKenzie, who had been volunteering in the care home, offered to record them.
Before Trevor died in 2012, he wrote a letter thanking those who helped him record the songs which he said had haunted him all his life, conveying his wish "that these few tunes from the long-forgotten isles can be preserved and given a future".
The last islanders left St Kilda on 29 August 1930 because life on the remote archipelago had become too difficult.
An album of lost songs from the evacuated Hebridean archipelago of St Kilda has gone straight to the top of the classical album chart.