A shutterbug of stone

  Roach stone with many 'Portland screws' England’s ‘Jurassic Coast’ is rightly famous.  Stretching along the English Channel coastlines of Devon and Dorset, it’s rocks bear witness to the entire Mesozoic – the Triassic, Jurassic and Cretaceous Periods (together known as the ‘Age of the Dinosaurs’) from East to West.  That’s a span of 185 million years, in the space between Exmouth in the west to Old Harry Rocks at Studland Bay, Dorset. Even if geology isn’t your thing, you’ve seen quite a few bits of it on film or television – West Bay, Bridport, is the setting for Broadchurch, Lyme Regis was home to Mary Anning (and of course to Trey), Kimmeridge Bay is famous for its fossils, Weymouth hosted the maritime events in the 2012 Olympics, and Lulworth Cove and Durdle Door are rightly famous. Chesil Beach and the Fleet are very important for their geomorphology and the lagoonal fauna of the brackish water in the Fleet. The Isle of Portland, tied to the mainland at the eas...

Following on  from the 'mintcake' Carrara marble I blogged about previously:  This column, in London's Royal Academy of Arts, is cipollino (little onion) marble - the green colouration comes from bands of chlorite and epidote.  Looking at it, it is easy to see how it got its name!  Both the ancient Greeks and the Romans used to quarry it, mainly for use as columns.  That still seems to be the case now; Westminster Cathedral (The Catholic one at Victoria) used it for the same purpose and, if memory serves, for a number of panels as well.   We happened to be at the RA for an exhibition and I was pleased to see this column there; I greeted it like an old friend.

  I was once sitting in a cathedral built from local limestones (from more than one source), and commented to my friend David that it would take some worthwhile heat and pressure to turn it into marble. He asked me, in total shock, whether one kind of rock can change into another.  The look on his face as he was asking was priceless!  I gave him the elevator pitch about metamorphic rocks, which have been transformed from one type of rock to another by the actions of heat and pressure.  Marble is one such metamorphic rock.  The purer the limestone was to start with, the purer (and more valuable!) the resulting marble.   Carrara Marble, one of the most famous stones in the world, was originally laid down as a pure marine limestone some 190 million years ago during the Jurassic, and then subjected to the aforementioned heat and pressure between 27 and 12 million years ago as the Apuan Alps formed.  The quarries, in Northern Italy, are enormous. ...

This, as the header of this post suggests, is Larvikite.  You've probably seen it cladding buildings and sparkling in the sun.  It is an intrusive igneous rock - one that is formed from magma that solidified underground. In this case, this happened near what is now Larvik (hence the name) in Norway. Larvikite is similar to granite in many ways but it has far less quartz than granite has. The feldspar minerals are iridescent because of some rather cool optical interference, rather like a kingfisher's feathers, and the iridescence varies as the angle you're looking at it from changes.  A polished slab is a so-and-so to photograph because the camera just looks through it to your reflection and you wind up with a selfie.* You also see it used in large, unpolished, blocks as coastal defences, and it's still very much worth a close look then. Incidentally, a chap by the name of Sir Montague Maurice Burton (of menswear fame) used Larvikite on the outside of his premises  ...