It was used quite a lot in the 19th century as mentioned, but fell out of common use by the middle of the 20th century. It actually features to the exterior of the Museum Building too, in medallion form, but it deteriorates very rapidly outside for obvious reasons, so it's more that just a little degraded in appearance today. It would appear Connemara's 'diversification' into rosary beads and whatnot signalled to their market that they weren't doing large scale slabs anymore, which seemingly wasn't the case - just there wasn't much demand.
In the 1960s, architect for the OPW Oscar Richardson very much admired the material, and sought its revival by contacting Connemara directly who confirmed they could indeed produce decent sized slabs. He suggested to Raymond McGrath to use it for flooring in the newly created and dubiously titled Marble Hall at Dublin Castle. And a fine floor it is too.
Very much of the Intercontinental Hotel era...
He also wanted to use it a little earlier on his infamous but very beautiful concrete spiral stairs at the Ãras at the end of the main corridor, but McGrath thought it would be too slippery, hence the mosaic finish employed - a material and art form Richardson also thought to be greatly undervalued at the time.