This page gives a short version of the story of Irish Blue Limestone.
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The Origin of Irish Limestone
The story of Irish Limestone began some 370 million years ago. At the time Ireland lay under a relatively shallow and warm sea. This provided ideal conditions for the precipitation of lime mud, incorporating clays and sands washed in from nearby landmasses. Bivalves were the most common fauna in the water.

For much of the following 45 million years the lime muds continued to form, though there were numerous variations and temporary breaks in the process.

About 325 million years ago conditions started to change. The drainage pattern in the adjacent landmasses altered and rivers began to carry more clays and sands into the sea. The accumulation of calcareous deposits ceased and, as the water became shallower, tropical forest began to grow in the area, helping to provide us with our current cover of vegetation and earth.

The Origin of the Irish Limestone Industry
During the Neolithic and Bronze Ages limestone was used as a construction material. Elaborate burial cairns, portal dolmens and passage graves made extensive use of limestone. Complex shapes including circles, spirals, diamonds, triangles and herringbones were carved into the limestone by craftsmen, and remain as examples of an art and craft form of the time.
Early stone masonry probably reached a pinnacle around 1000 AD with the construction of Round Towers through the country.
The latter part of the twentieth century has seen major changes to the extraction of stone, and the manufacturing and finishing capability of the industry, due in part to the emergence of diamond technology.

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Popular surface finishes applied to limestone include:

Ground
Flat even surface with fine circular scoring that may be difficult to identify in some finishes.
Colour: Pale, grey-blue on the coarser grit finishes but becoming darker where finer grits are used.
Application: Internal and external cladding and ashlar. Sills, steps, lintels, capping, gravestones and kerbs. May also be used for internal and exterior floor tiles.

Machine Chiselled
Flat parallel even tooling tracks separated by narrow lines of grey split stone. Various pattern densities are used.
Colour: Pale grey-blue depending on the density of the tooling.
Application: Ashlar for sills, steps, lintels and piers. Monuments and grave kerbs. Internal and external cladding.

Mechanical old Cut
The surface is covered in closely spaced short irregular chisel marks.
Colour: Pale Grey-blue with the contrast between the chisel marks and the rough stone only apparent at close range.
Application: Floor tiles, setts, pavoirs and kerbs, where it produces a good non-slip surface.

Hammer Dressed
Surface pattern of irregular spaced circular impact points, 1-3mm in depth.
Colour: Pale grey-blue with whitish flecks.
Application: Suitable for interior and exterior work and as a decorative finish or as a non-slip surface.

Honed
Even matt surface with no tooling marks.
Colour: Dark, blue-grey but will exhibit tone variations depending on the part of the quarry the stone came from.
Application: Internal applications such as cladding, steps, sills and floor tiles. It may also be used in furniture pedestals, tops for vanity units and counters.

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