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Light brownish grey sandstone

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{{OR/15/053}}
Castle Sween is believed to be the oldest castle still standing in Scotland. It is located on a low rocky ridge on the east shore of Loch Sween, in Knapdale. The site would have provided the occupiers with an extensive view of Loch Sween, and as far as Jura.

==Layout and building chronology==
The castle is comprised of a massive Curtain Wall with two towers: the West Wing Garderobe Tower, and the Northeast Tower. The entrance to the Castle is in the middle of the South Curtain Wall. The inner courtyard is comprised of ruinous East and West Ranges, and a Well. A timeline of construction and alterations for Castle Sween is presented in Table 2.

{| class="wikitable"
|+ Table 2 Timeline of construction and alterations in Castle Sween 
''Information from RCAHMS, (1992) ''<ref name="RCAHMS 1992">RCAHMS. 1992. ''Argyll: an inventory of the monuments'', Vol. 7 Mid Argyll and Cowal, Medieval and later monuments. Bell and Bain Ltd: Glasgow; 246–7</ref> 

| ! scope="col" style="width: 150px;" | '''Date'''
| ! scope="col" style="width: 125px;" | '''Action'''
| ! scope="col" style="width: 350px;" | '''Location or masonry element'''
|-
| c.1200
| Construction
| Small courtyard flanked by ranges
|-
| Early 13th C
| Construction
| Upper parts of Curtain Walls
|-
| 13th C
| Construction
| West Wing (single-storey, outside West Curtain Wall)
|-
| 13th C
| Construction
| Northeast Range
|-
| Early 14th C
| Construction
| West Wing Garderobe Tower (3-storeys)
|-
| 15th C
| Construction
| Northeast Tower with kitchen and chambers (outside North Curtain Wall)
|-
| 15th C
| Construction
| East Range with Great Hall (2 to 3 storeys)
|-
| 15th C
| Construction
| West Range
|-
| 16th C
| Construction
| Vaults in Northeast Tower and East Range
|-
| Mid- to Late- 17th C
| Abandoned
| All
|-
| 1985–9
| Repair
| All, major consolidation works
|}

==Building stones==
===Walling stone===
Several different types of metamorphosed rock have been used as walling stone in Castle Sween, including metasedimentary rocks (metamorphosed sandstone and mudstone) and metamafic (igneous) rocks. The walling is generally coursed rubble style. Larger, sometimes rounded, blocks commonly of metasandstone are held with smaller, tabular pinnings of metamudstone and metamafic rock (Figure 9b); the latter rock types also occur in a range of shapes and sizes throughout the rubble walling. These rock types occur in rock outcrops by the castle that have obviously been quarried in the past, and much of the walling stone was probably sourced from outcrops and superficial deposits near to the castle.

A sample of the metamafic rock was collected from a small block that had become detached from the rubble walling. A thin section was prepared and is described in [[OR/15/053 Appendix 1 – Sampling and petrographic descriptions |Appendix 1]]. The rock is foliated metamafic rock, almost certainly from an intrusion in the Dalradian Supergroup. This rock type is mapped immediately underlying Castle Sween on BGS geology maps. The bedrock c.200 m to the southeast of the castle is assigned to the Crinan Grit Formation (which consists mainly of metasandstone), and the metasedimentary rocks in the walling will have come from this unit.

===Decorative stone===
====''Flaggy metamafite''====
Tabular blocks of flaggy, strongly foliated, greenish-grey metamafite have commonly been used to form lintels and sills around door and window openings, some of which can also feature sandstone quoins (Figure 8c). This flaggy metamafic rock has similar geological characteristics to the stone at Doide quarry ([[OR/15/053 Appendix 1 – Sampling and petrographic descriptions |Appendix 1]]). This observation agrees with the assessment by Walker (2000)<ref name="Walker 2000">WALKER, F A. 2000. ''The buildings of Scotland: Argyll and Bute''. (London: Penguin Group.) ISBN 0140 71079 5</ref>, who cited Doide quarry as a source of decorative stone used in Castle Sween:

''“In medieval times the quarries at Doide on Loch Sween supplied stone slabs of the green, chlorite-albite schist for numerous crosses and tombstones, and it was also used in building for pinnings and lintels, as at Castle Sween… This outcrop has vertical joints which allow the rock to be split into slabs a few centimetres thick. It was easily carved and was the preferred stone for this purpose for many centuries”.''

However, the rock is essentially closely similar to some of the walling stone, and some at least may have been sourced from one or more other sites in the vicinity.

[[Image:OR15053fig8.jpg|thumb|center|700px| '''Figure 8''' Plans for Castle Sween with periods of construction and alteration. Source: RCAHMS (1992) <ref name="RCAHMS 1992"></ref>, pages 246–7. ]]

====''Light brownish grey sandstone''====
Blocks of uniform, fine- to medium-grained, light brownish grey sandstone have been used to form quoins and dressings, including those forming the archway at the main entrance to the castle. (Figure 9a, d). All of the sandstone dressings in the castle appear to be of the same stone, which is present in all of the stages of construction. In some blocks the sandstone contains thin quartz veins, iron-stain banding and concretions. Many of the sandstone dressings are only around 20 cm deep, and are placed around doors and window surrounds as well as quoins. Some sandstone blocks are experiencing rapid material loss (through scaling and granular disintegration), and some show signs of alveolisation (salt-weathering) in places Figure 9b, d).

[[Image:OR15053fig9.jpg|thumb|center|600px| '''Figure 9''' Decorative stone in Castle Sween.
 
''a – detail of weathered sandstone block on the E side of the main doorway in the SW elevation of Castle Sween. b – sandstone quoins showing alveolisation (deep pitting), at the SE corner of Castle Sween. c – a lintel and sill formed of tabular blocks of metamafite on the NW-facing elevation of the N side of Castle Sween. d – sandstone dressings around the main doorway in the SW elevation of Castle Sween.'']]

A thin section of the light brownish grey sandstone was prepared from a fragment of stone that had fallen to the ground. The thin section reveals that the stone contains rounded, wind worn-grains of metamorphic rock that are partly enclosed in a mineral cement of calcite ([[OR/15/053 Appendix 1 – Sampling and petrographic descriptions |Appendix 1]]). The wind-worn sand grains indicate the sandstone was deposited in a desert environment, and therefore is probably of Permian or Triassic age. The pale grey colour is unusual for Permian or Triassic sandstone, but greyish white Permian-Triassic sandstone with a calcite cement has been described at Muasdale on the west coast of Kintyre ([[OR/15/053 Possible sources of decorative stone in Argyll galley castles #Permian-Triassic sandstone |''see'' Permian-Triassic sandstone]]). Based on the available evidence, this is the likeliest source of the sandstone in Castle Sween.

==References==
<References/>

[[Category: OR/15/053 Provenance of building stones in four 'galley castles' in Argyll | 05]]

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