Several of us went to Winterthur on Saturday and among other things, noticed stones that had been drilled several inches deep, hole diameter ~3/8 to 1/2", said penetrations spaced every few inches. If you look at my photos here, you’ll see one of a garden stone exhibiting these marks. What is the purpose of these regularly appearing drillings? To set up a fracture line when the stone is cleaved? Over to you, teeming millions.
Yep. On a smaller scale, I’ve split paving stones by just drilling a series of holes and pounding in hardened cut nails as wedges.
When we took a tour of a marble finishing shop, they said the holes are for moving the large pieces around. they were hung on chains, awaiting their turn on the big stone saw that cut them into managable sizes.
That would make sense if there were only two or three holes. If you’ve gone to the photo link, although the detail isn’t that good, a four foot long stone will have easily 16 drill marks along the long dimension of the stone.
Here’s a link with some pictures.
That’s basically what we observed. Thanks Hunter Hawk.
Wasn’t Homer Simpson a Stonecutter for a while? He had the mark IIRC.
I told you we’d get a quick answer! 
Very true, indeed. 
I quite often see this pattern of drilling on larger blocks of stone dumped in the sea as part of sea defences, breakwaters or harbour walls - I’m sure they are done when the rock is quarried and I think they are drilled to force a crack (started by an explosive charge somewhere nearby) to propagate along a certain line (I initially thought they might all have been for the placement of explosives, but their sheer number would seem to make that overkill.
Damn, I could hum that little ditty all night long. 
They are for the placement of explosives. There are nonexplosive ways of quarrying that use expanding clays (IIRC). In some road cuts you can still see the bore holes. There was a thread in here about Rockport Mass, where you can still see some of holes used for quarrying the granite.
The pieces put in the holes are called wedges and shims. They are still available from Trow and Holden - If you really want to do your own stone work.
To quarry the stone you first drill the holes. The size and separation of the holes depends on the size of the wedges and shims, which depends on the size of the block you want to cut. Put a wedge and shim in each hole. Place the shims so they are perpendicular to the direction of the crack you want to create.
Bang away - start at one end and tap once at each wedge working your way down the line.
When the rock rips apart - raise your right hand. Put it on your left shoulder. Give yourself a well deserved pat on the back.
I’ve seen the stonework in question, and I know about blasting bores - I’ve seen them quite often too. In this case, the holes were very much not for blasting but for the purpose Hunter Hawk confirmed.
dances, I coulda toldja if you’d asked…
How can you tell they’re not blast-related? They look exactly the same to me - the rocks I’ve seen as part of the sea defences showed exactly the same kind of closely-spaced parallel bore-holes as seen in the split block in Hunter Hawk’s link. The rocks for these sea defences can’t possibly all have been split by hand.
Far, far too close together, on two different planes of the rock, and far too shallow.
That’s how.
The parallel holes I’ve seen in the sea defence rocks are also numerous and close together - a couple of inches apart at most. There are also larger-bore, more widely-spaced holes (which I think were the ones in which the explosive was placed). Maybe I’m wrong, but it just seems like nobody would go to the bother of carefully hand-splitting a very large collection of rocks just to dump them in the sea.
I’ve seen them all over the place, but the ones I’m particularly thinking of are at Hurst Point, near Christchurch, UK. Maybe I’ll pop out there at the weekend and take some pictures.
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- It’s from wedges and leaves, as someone already noted. Quarried blocks of stone always have these marks at least at first, because this is how the block is first broken loose of the ground. Explosives are not used to quarry architectural stone, and explosive boreholes are made 2-3+ feet deep anyway. After the block is loose it can be cut other ways, a diamond-wire saw is usually used to produce smooth blocks with minimal waste. A place named Johnson Atelier (a quarry/stone dealer in NJ) has one of the largest diamond-wire saws in the US, it’s big enough to saw a stone up to something like 7 feet thick, 12 feet wide and 35 feet long.
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- It’s from wedges and leaves, as someone already noted. Quarried blocks of stone always have these marks at least at first, because this is how the block is first broken loose of the ground. Explosives are not used to quarry architectural stone, and explosive boreholes are made 2-3+ feet deep anyway. After the block is loose it can be cut other ways, a diamond-wire saw is usually used to produce smooth blocks with minimal waste. A place named Johnson Atelier (a quarry/stone dealer in NJ) has one of the largest diamond-wire saws in the US, it’s big enough to saw a stone up to something like 7 feet thick, 12 feet wide and 35 feet long.
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OK, I went to the beach yesterday and took some photos; there’s a truly gigantic jumble of rocks like this, this and this reinforcing/protecting a length of shingle beach about a mile long; must be thousands of tons of boulders, mostly granite (I think), ranging from the size of a refrigerator to the size of a car. At least half of them have these visible traces of drill marks, spaced about two inches apart.
Clearly they are not (or not all) what I originally suggested - holes drilled to propagate a crack started by explosives - this is evidenced by pieces like this, where the same technique has been used more than once to create several faces.
However, I still find it hard to accept that these blocks have been split by the laborious process of hammering in wedges sequentially by hand - the sheer quantity of them (like I said, thousands upon thousands of tons) would seem to make that an enormous undertaking, but there’s also this - here we see a split that has not followed the line of drilled holes (presumably folloing a natural fault instead), BUT - I don’t think we’re looking at the underside of the piece, as there is no spalling around the holes and if we’re looking at the top side, wedges wouldn’t appear to have been used (as thy’re not still stuck in the holes and there’s no evidence of the holes being damaged by them).
These holes must have been drilled in some kind of jig - they are far too uniformly-spaced and precisely parallel for anything else; is there not some machine that splits blocks in this way? i.e. drilling closely spaced holes, then using them to propagate a crack, but not by individual wedging?
I actually meant breakout, when I said spalling.
Cool pix, mangetout. (Your third link didn’t work, btw.)
No answer – but one difference between your rocks and the ones dances was asking about is that it looks like the lines (half-holes?) go all the way down, whereas in the others, the holes went in maybe an inch or two.