Sarsen stones are the very large stones that forms the outer circle at 
Stonehenge.
These stones are a very hard type of sandstone. Now to give one a clear idea as to how hard this particular stone is we will take a look at the Mohs scale.
The Mohs scale is simply a measurement used to measure the surface resistance to abrasion of any hard substance.
That just means that if we take a hammer and bash the stone how much will it resist before we can knock a chunk off it.
Sarsen stone measures a seven (7) on the Mohs scale.
Now, if we compare the surface resistance of sarsen stone to that of steel we find that steel measures 6,7 on the same scale.
So, we now know that sarsen stone is a very hard stone and we can appreciate how difficult it must have been to shape the stone with ancient tools.
Sarsen stones were worked and dressed with other sarsen stone which were round balls of stone known as mauls. The mauls were of various sizes and can today be viewed at the Salisbury museum.
From exploration at Stonehenge it would appear that there were 30 stones that were used as “uprights”.
Of these “uprights” 29 of them were shaped to the same basic size.
When the sarsen “uprights” were placed into position they were then capped with a line of sarsen stone lintels.
The lintels weighs up to seven tons ( 7,000kg.) each.
To fix the lintels securely in position thirteen feet or 4m. above the ground these lintels were locked together like pieces in a jigsaw.
The lintels were held in place on the upright sarsen stones by mortice-and-tenon joints which was carved out of the solid stone.
The lintels in the circle were then locked end-to-end by a method known as vertical tongue and groove joints.
The jointing techniques used on the sarsen stones are all from the wood joiners craft.
Another amazing feature is that the lintel circle of sarsen stones were shaped to follow the curve of the circle which is both a design and engineering feature.
Merlin @ Stonehenge
The Stonehenge Stone Circle Website
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