Stone Materials in Ancient Akrotiri - A Short Compilation

It is not surprising that the bulk of material consists mainly of volcanic rocks from Thera which are found nearby the site. However some rocks of metamorphic origin are also found which are known today from only a small number of outcrops, thus indicating a wider distribution beneath the upper pumice layer on Thera.

Several rock types are not known from Thera, pointing to Crete and Melos as the source for these materials.

The most probable sources of the different materials are given in a map of the southern part of Thera.

1. VOLCANIC MATERIAL FROM THERA

1a. Redbrown to black scoria

This porous, slightly flattened pyroclastic material with rugged and stuffed surface is the main constituent of the walls of the buildings. Rocks of this kind outcrop east of Cape Mavro as a few m. thick layer beneath the upper pumice. Chemically (see below) and mineralogically this material is identical with redbrown and black scoria fragments from the walls of the West House:

 +) total iron

Though not favourable from the point of view of the stability of the buildings this material was obviously attractive because of the large resources, easy exploitation (the scoria is only slightly baked together) and position near the shore line helping in transport by water.

1b. Redbrown and black porous lava,

well worked to rectangular blocks up to 0.5 m in length, were used as corner-stones, front-stones, window-cases and stairs (for example some corner-stones and windows of the West House). Mineralogically and chemically this material is very similar to the red brown and black scoria (see chemical analysis above) and is probably from a massive layer of lava of the same origin.

1c. Pebbles of different volcanic rocks

up to almost 1 m. in length were used for wall construction. They could have come from the nearby beach. Small pebbles of the size of some cm. were used for paved flooring, using a calcitic / clayish cementing material (for example room D1).

1d. Fine grained whitish and greenish tuff,

sometimes with angular rock fragments. This tuff was used as rectangular blocks for building stones, window-cases and stairs (for example Ashlar Building 4 A, staircase from D5 to D7).

This material is found in a large area some 100 m. west of the site, and consists of slightly layered dacitic tuff (Günther 1970) altered by ancient fumarolic activity (Reck 1936; Schorin 1972). It was seldom used for stone vessels, etc.

1e. Ignimbrites,

pyroclastic material of a deep brown colour, sometimes densely welded, with black obsidian-like lenses. The material is easy to work and was used as front-stones, corner-stones, stairs, window-cases and door sills (for example, building complex x, southwest of complex G, rooms 2 and 5). It was seldom used for stone vessels etc. The "bath" in room 3 of the West House is an exceptional example. The material represents the upper ignimbrite which covers a large area on Thera beneath the upper pumice (Pichler & Kussmaul 1972).

Today a good exposure is found north of the village of Akrotiri at the rim of the caldera. The ancient quarries lay probably in the immediate vicinity of the excavation site because this ignimbrite is found below the foundation level of the oldest part of ancient Akrotiri, as can be seen near room D8.

1f. Hornblende bearing dacite.

This light grey, dense material with small black crystals of hornblende and pyroxene was seldom used in building though outcrops are found nearby the site (another occurence is situated at Cape Akrotiri). This is probably caused by the polygonal shape of the natural material giving poor stability to the walls, and the huge effort of working these dense stones. Only some angular fragments were found in the walls and 3 big door sills are worked from it (in rooms D5, D1 & G5). However this material has been used for a lot of marvellous stone vessels.

1g. Floor slabs of dense volcanic rocks.

They are light to dark grey, about 1 to 3 cm. thick and sometimes more than 1 m. in diameter. Their platey shape is of natural occurence. Seven samples (from the House of the Ladies, Well-Built-Mansion, D-Complex, West House) showed an identical mineralogical composition with characteristic xenomorphous-phenocrysts of olivine. Such material was described by Pichler & Kussmaul (1972) as characteristic for the Akrotiri II volcanic succession. Another occurence of olivine-bearing volcanites is found in the lavas of the Skaros volcano, north of Fira.

2. VOLCANIC MATERIAL FROM OUTSIDE THERA

Many fragments and a bigger block of obsidian were found during the excavations. Though obsidian-like material is found in some volcanic rocks on Thera its bad quality and small, patchy occurences makes it unusable for tools etc. Chemical investigations (Puchelt, unpub. data) point to Melos as the source for the obsidian.

NON-VOLCANIC MATERIAL

3. Limestones and Marbles.

Macroscopically different types can be distinguished.

3a. Pebbles of marble-like limestone

up to 0.5 m in diameter were found in the Telchines Road and in the walls of some buildings. Fabric and colour resemble those of the limestones from Gavrilos Hill and Profitis Ilias area: streaky whitish and reddish coloured, fine grained with poor layering. Small fragments were used for paved flooring (for example in room D8).

3b. Black and white banded marble

used for a stone vessel, and a pebble-like fragment of red and white banded marble come very probably from Crete (P. Warren, pers. comm.). of shelly limestone, stone

3c. Different types of marble of unknown origin.

A small fragment of shelly limestone, a big stone vessel of reddish, dine grained marble-like limestone in the House of the Ladies etc.

METAMORPHIC SCHISTS

4a. Chlorite schists.

These are light green, fine grained schists consisting mainly of chlorite, sericite and quartz. This material was used for floor-slabs, door sills, stairs and covers for pithoi, though not commonly. Today this type of rock is exposed inside the caldera at Athinios, probably not available to the people of ancient Akrotiri. This indicates a larger occurence of the chlorite schists now covered by the pumice.

4b. Very seldom one finds fragments of reddish to violet phyllitic schists very similar to the phyllites of the Sellada.

5. Serpentinites.

This material was used only for stone vessels and oil-lamps. There seem to be different kinds of serpentinites, some dark-green and patchy, some almost homogeneous black, some very rich in mica, some heavily brecciated. Serpentinites are known from several localities on Crete (Warren 1969) and this is probably the origin of the serpentinites found in the site.

6. Gypsum.

Gypsum was used for small vases and other stone vessels. The material is not known from Thera except as small efflorescences from altered volcanic material (Schorin 1972). Of more interest are the gypsum slabs from the West House, room 1, and from the House of the Ladies. These floor slabs are up to 3 cm. thick and about 0.5 m. in diameter and are corroded on both sides by water.

As seen in thin section they consist mainly of gypsum, coarsely grained, a small amount of calcite and quartz and streaky accumulations of clay minerals. The material contains a lot of fluid inclusions of different hydrocarbons. Compared with several samples of gypsum from Crete there is a remarkable conformity in mineralogical composition, fabric and fluid inclusions with one sample from a gypsum quarry south of the palace of Knossos.

7. Other materials.

Small fragments of some other material of unknown origin were found: two fragments of rock crystal, a small square of steatite, a pebble-like fragment of granodiorite and a small fragment of mica-rich sandstone.

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