Slate

Otta Phyllit Pillarguri

Otta Phyllit Pillarguri is one of the most characterful Scandinavian dimension stones — a Precambrian phyllite from the Pillarguri mining district near Otta in the Norwegian region of Gudbrandsdalen (Innlandet). The riven variant shows a deep anthracite to black ground tone with characteristic intergrown actinolite and hornblende mineral needles, scattered across the surface like a vault of stars in silvery, shimmering strokes. At ROSSITTIS we fabricate Otta phyllite into classic Norwegian external floor coverings, stairs, facade elements, roofing slates, window sills, skirtings and carefully planned interior fit-outs with a powerful Nordic dimension-stone character.

Petrographically a Precambrian metamorphosed slate (phyllite) – the metamorphic intermediate between fine-grained slate and coarser-grained mica schist. In the marble trade it is classically listed as “slate”, because the material is fabricated for roofing and floor applications on account of its cleavability. Characteristic are the intergrown actinolite mineral needles, known in the trade as “Otta stars”.

Slate Norway 2.790 kg/m³

Available as: Slabs, Skirting, Treads & risers

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About Otta Phyllit Pillarguri

Background. Otta phyllite is among the most tradition-rich Norwegian dimension stones and is regarded as the “national stone” of Norway. The deposits lie in the Pillarguri and Sel mining district near Otta in the historic region of Gudbrandsdalen (today the province of Innlandet, central Norway). The quarries have been worked for centuries; in the modern mining operation, Minera Skifer is the principal producer and fabricator. Otta phyllite defines numerous significant Norwegian buildings, among them the Royal Palace in Oslo, Trondheim Cathedral (Nidarosdomen), the Norwegian parliament (Stortinget) and most of the classic sacred buildings. Internationally, Otta has been used for the Holocaust Memorial in Berlin (Eisenman, 2005), for numerous Scandinavian municipal buildings and for contemporary premium architecture.

Geology. Petrographically, Otta phyllite is a Precambrian metamorphosed slate (phyllite) — the metamorphic intermediate between fine-grained slate and coarser-grained mica schist. Its mineralogy comprises quartz, muscovite, chlorite and — as its characteristic hallmark — intergrown actinolite mineral needles (a variant of the hornblende family). In a polished section these actinolite needles are visible as fine silvery, shimmering strokes and rods, distributed across the dark phyllite matrix like a vault of stars or an effect of falling rain. Geologically they are part of a metamorphic mineral fabric known in the stone trade as “Otta stars”. The grain size of the phyllite matrix is very fine (≤ 0.1 mm); the actinolite needles are 1–10 mm long. In the stone trade the material is classically listed as “slate”, because its cleavability makes it suitable for roofing and flooring applications.

The Pillarguri selection. “Pillarguri” denotes a particular quarry area within the Otta mining district. There are several Otta selections with differing mineral density, actinolite size and cleavage character; Pillarguri is among the highest-grade selections, with particularly pronounced actinolite needles and even cleavage quality.

Appearance. The ground tone is a deep, slightly warm-toned anthracite black — not a pure coal black, but a characterful dark tone with subtly greenish-grey nuances. Distributed across the ground are the characteristic silvery, shimmering actinolite mineral needles in varying lengths and directions — they give the material its unmistakable appearance. Occasional rusty-brown accents also occur, produced by embedded pyrite or iron mineral inclusions, and give the slab additional warmth. The finishes currently available from stock are listed in the »Finishes« block further down this page.

Technical values. Otta phyllite is a technically outstanding dimension stone. Bulk density is around 2,790 kg/m³, water absorption a very low 0.19 %, compressive strength about 218 MPa and flexural strength around 48.6 MPa — the flexural strength of 48.6 MPa is exceptionally high and makes the stone extremely load-bearing outdoors and in floor applications. Mohs hardness 4–6 (depending on mineral composition). Frost resistance is clearly given, and acid resistance is good (the material contains no calcite). Its natural cleavability allows very thin slabs (1–3 cm) for roofing and facade applications.

The ROSSITTIS range. The finishes currently available from stock are listed in the »Finishes« block further down this page. From these we fabricate external floor coverings in large or tile formats, pool surrounds, stairs with treads and risers, facade elements, roofing slates, wall copings, window sills, skirtings and carefully planned interior fit-out components.

Comparison. Within the Scandinavian slate spectrum, Otta Phyllit Pillarguri is one of the most prestigious materials alongside Oppdal quartzite and Alta slate. Compared with Spanish or English roofing slate selections, Otta is markedly stronger in grain and, with its characteristic actinolite needles, unmistakably identifiable. Compared with Italian phyllites (Anden phyllite matrix), Otta is darker and has a more pronounced mineral texture. Outdoors, Otta phyllite is one of the most robust European dimension stones.

A frank assessment. Otta Phyllit Pillarguri is a choice for clients and architects seeking a powerfully Nordic dimension stone with outstanding technical load-bearing capacity and an unmistakable mineral identity. It is not an elegant, smooth marble for living spaces — its strength lies in its suitability for external use, its riven dimension-stone character and the characteristic actinolite star structure. For classic Norwegian architecture, contemporary Alpine buildings, pool surrounds, external stairs, facades and prestige entrance areas it is one of the best European slates and phyllites.

In stock

Current availability from our warehouse.

42 slabs in stock · plus 14 blocks

Thicknesses: 1–3 cm · Finishes: Satin-honed, calibrated, Honed C600, calibrated, Riven and more · Available as: Slabs, Skirting, Treads & risers

Updated daily from our live stock.

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Technical data

Guide values for the stone type, taken from manufacturer and test reports. Natural stone is a natural product — individual batches and slabs can differ. For critical applications, request slab-specific test data.

Rohdichte 2.790 kg/m³

Druckfestigkeit 218,3 MPa

Biegezugfestigkeit 48,6 MPa

Wasseraufnahme 0,19 %

Säurebeständig Nein

Finishes

Otta Phyllit Pillarguri is available in a range of finishes. The finish affects appearance, feel and the care it needs.

Satin-honed, calibrated

As for the satin finish (a brushed matt surface with subtle depth), but additionally with a calibrated reverse: the underside of the slab is ground flat for an even thickness and simplified installation. Recommended for floor areas, stair treads and bonded fixings that demand precise dimensional accuracy.

Honed C600, calibrated

As for honed C600 (a very fine honed finish with clear colour intensity and barely visible honing marks), but additionally with a calibrated reverse: the underside of the slab is ground flat for an even thickness. Recommended for high-quality floor areas and wall claddings that demand precise dimensional accuracy.

Riven

The surface corresponds to a natural splitting of the rock — the layered characteristic typical of slate comes fully into its own. A matt, rough appeal with high slip safety and an originally natural effect. Recommended for outdoor areas, wall claddings and heavily used paved surfaces.

Honed C600

A very fine honed pattern with a C600 grit — the level surface shows a clear colour intensity with honing marks barely visible any more, almost like polished depth in a matte effect. More care-intensive than polished, yet visually very close to polished elegance — a refined choice for high-quality interior surfaces.

Care & fabrication

Cleaning. In everyday use, warm water, a soft cloth or a clean mop and a neutral to slightly alkaline pH stone cleaner are sufficient. Soapy slate and phyllite care products and mild general-purpose cleaners are suitable. Otta phyllite is more acid-proof than marble (it contains no calcite); brief exposure to acid is not a problem.

Do not use. Avoid concentrated acids (sulphuric, hydrochloric, nitric), concrete and rust removers and strongly alkaline industrial cleaners. Do not use film-forming care products (waxes, oils) on the riven surface — the natural mineral character depends on an open, breathing surface.

Sealing. Usually not required outdoors. Indoors, a silane-polysiloxane sealer can be sensible on sensitive internal surfaces to reduce the uptake of grease and pigments.

Kitchen. Otta phyllite is technically suitable as a kitchen worktop, but aesthetically it suits rustic or Scandinavian-minimalist schemes rather than others. Use chopping boards; trivets for hot pans are standard practice. Acids such as wine, lemon and tomato are not a problem (phyllite is acid-proof).

Bathroom. Very well suited in the bathroom as a floor covering, wall cladding and in showers. Anti-limescale sprays and bathroom cleaners are not a problem in normal use. The riven variant is slip-resistant in the shower area.

Floors and stairs. The classic application. The riven variant with its pronounced mineral texture is the first choice for external floors and heavily used internal areas. Honed C600 is suited to quieter internal schemes.

Outdoors, pools and facades. Fully suitable. Frost-resistant, acid-proof, with a high flexural strength of 48.6 MPa. Classic Scandinavian external applications (pool surrounds, external stairs, facades, roofing slate).

Repair. Deeper damage can be made good with a tinted polyester-resin-based phyllite filler. With riven slabs, individual pieces can be replaced, because the natural scatter of the mineral needles conceals differences between individual slabs well.

Fabrication. When working Otta phyllite dry (cutting, grinding), dust extraction should be used — as with all slates containing mineral fibres. The actinolite mineral needles in the commercial Otta selections are controlled and are not classified as asbestiform; the recommendation to use dust extraction is standard practice in all stone fabrication and is not a risk specific to Otta.

Frequently asked questions

What is Otta Phyllit Pillarguri geologically?

Petrographically a Precambrian metamorphosed slate (phyllite) — the metamorphic intermediate between fine-grained slate and coarser-grained mica schist. Its mineralogy comprises quartz, muscovite, chlorite and, characteristically, intergrown actinolite mineral needles (a variant of the hornblende family), visible in polished section as fine silvery, shimmering strokes.

What are the “Otta stars”?

The characteristic silvery, shimmering mineral needles in the phyllite matrix are known in the stone trade as “Otta stars”. They are intergrown actinolite needles (hornblende family), 1–10 mm long, distributed across the dark ground like a vault of stars or an effect of falling rain.

Where does Otta Phyllit Pillarguri come from?

From the Pillarguri and Sel mining district near Otta in the Norwegian region of Gudbrandsdalen (province of Innlandet, central Norway). The quarries have been worked for centuries; Otta phyllite is regarded as the “national stone” of Norway and defines the Royal Palace in Oslo, Nidarosdomen in Trondheim, the Stortinget parliament building and the Berlin Holocaust Memorial.

What technical values does Otta Phyllit Pillarguri have?

Bulk density around 2,790 kg/m³, water absorption only 0.19 %, compressive strength 218 MPa, flexural strength an exceptional 48.6 MPa, Mohs hardness 4–6. Frost resistance is clearly given. These values make Otta one of the most mechanically load-bearing dimension stones in Europe.

Which finishes does ROSSITTIS supply?

The finishes currently available from stock are listed in the »Finishes« block on this page.

Are the actinolite mineral needles a health concern?

Actinolite belongs to the hornblende mineral family and can in theory occur in asbestiform fibre lengths. In the commercial Otta selections from Pillarguri, however, the mineral inclusions are controlled; the typical actinolite needles do not occur in asbestiform fibre lengths and are classified as harmless. When working Otta phyllite dry (cutting, grinding), dust extraction should be used — as with any natural stone fabrication.

Is Otta phyllite suitable for external surfaces, facades and roofs?

Yes — this is one of its core domains. With its outstanding frost resistance, acid resistance, flexural strength of 48.6 MPa and natural cleavability, Otta is one of the best European dimension stones for external paving, pool surrounds, facade panels, roofing slates and external stairs. Classic Scandinavian architecture.

Otta phyllite or classic roofing slate?

Otta phyllite appears stronger and more mineral, and is identifiable by its characteristic actinolite stars. Classic roofing slate (Spanish roofing slate, for example) is usually finer-grained and more homogeneous, without visible mineral needles. Otta is the more prestigious and more expressive dimension stone; classic roofing slate is the more economical option for pure roofing use.

What does Otta Phyllit Pillarguri cost?

The price depends on the batch, thickness, surface finish and fabrication — with natural stone there is no serious flat rate per square metre. Business customers see prices once their B2B account is activated; private customers receive a complete quote through a fabricator near them.