# Under What Circumstances Does Rock Form Hexagonal Piles? **URL:** \ **Category:** Factual Questions\ **Created:** [March 30, 2013, 12:04pm UTC](https://boards.straightdope.com/t/under-what-circumstances-does-rock-form-hexagonal-piles/654345 "2013-03-30T12:04:54Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [March 30, 2013, 12:04pm UTC](https://boards.straightdope.com/t/under-what-circumstances-does-rock-form-hexagonal-piles/654345/1 "2013-03-30T12:04:54Z")
A friend came back from Northern Ireland-he took some neat pix of the “giants Causeway”-which is a unique rock formation. It is a big mass of basaltic rock, where the rock has split into hexagonal piles. They are so regular looking, it seems like they cold have been man-made. I have also seen these things in other places-the “Devil’s Post Pile” (Wyoming) has rock that looks similar. What causes this to happen? I know the hexagon is a shape that allows for maximum packing (bees use them for honey storage)…but why don’t they form squares or triangles? ---
**Author:** ![Baron\_Greenback](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/baron_greenback/32/48_2.png) [@Baron\_Greenback](https://boards.straightdope.com/u/Baron_Greenback)\ **Post date:** [March 30, 2013, 12:24pm UTC](https://boards.straightdope.com/t/under-what-circumstances-does-rock-form-hexagonal-piles/654345/2 "2013-03-30T12:24:00Z")
The Giant’s Causeway isn’t a unique formation, there’s another one just across the water. > **[Fingal's Cave](https://en.wikipedia.org/wiki/Fingal%27s_Cave)** > > Fingal's Cave is a sea cave on the uninhabited island of Staffa, in the Inner Hebrides of Scotland, known for its natural acoustics. The National Trust for Scotland owns the cave as part of a national nature reserve. It became known as Fingal's Cave after the eponymous hero of an epic poem by 18th-century Scots poet-historian James Macpherson. > Fingal's Cave is formed entirely from hexagonally jointed basalt columns within a Paleocene lava flow and is similar in structure to both the Giant's Ca... Ahem, as you noted in the OP. Carry on. ---
**Author:** ![Foggy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foggy/32/1082_2.png) [@Foggy](https://boards.straightdope.com/u/Foggy)\ **Post date:** [March 30, 2013, 2:05pm UTC](https://boards.straightdope.com/t/under-what-circumstances-does-rock-form-hexagonal-piles/654345/3 "2013-03-30T14:05:30Z")
From the wiki link: > [@](#): > > In all these cases, cooling on the upper and lower surfaces of the solidified lava resulted in contraction and fracturing, starting in a blocky tetragonal pattern and transitioning to a regular hexagonal fracture pattern with fractures perpendicular to the cooling surfaces.[3] As cooling continued these cracks gradually extended toward the centre of the flow, forming the long hexagonal columns we see in the wave eroded cross-section today. Similar hexagonal fracture patterns are found in desiccation cracks in mud where contraction is due to loss of water instead of cooling.[4] It’s just the way the lava cooled. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [March 30, 2013, 2:06pm UTC](https://boards.straightdope.com/t/under-what-circumstances-does-rock-form-hexagonal-piles/654345/4 "2013-03-30T14:06:53Z")
> [@ralph124c](#): > > I have also seen these things in other places-the “Devil’s Post Pile” (Wyoming) has rock that looks similar. That Wyoming site is [Devils Tower](http://en.wikipedia.org/wiki/Devils_Tower). [Devils Postpile](http://en.wikipedia.org/wiki/Devils_Postpile_National_Monument) is in California. The semi-regular columns of basalt result from the slow cooling of homogenous lava. [This site](http://geomaps.wr.usgs.gov/parks/depo/dpgeol5.html) has a good explanation. And note that while the number of sides is often 6, other shapes are found (including triangles and rectangles). From the link: > [@](#): > > The columns have various numbers of sides, as indicated by a sample of 200 posts: 4 sides, 2%; 5 sides, 37%, 6 sides, 55%, 7 sides, 5%. A few columns have only three sides. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 30, 2013, 2:22pm UTC](https://boards.straightdope.com/t/under-what-circumstances-does-rock-form-hexagonal-piles/654345/5 "2013-03-30T14:22:40Z")
Note that those other numbers of sides aren’t regular polygons; they’re regular hexagons that are further broken in some way.