All that glitters

....is not gold. It's probably mica!
I was being optimistic thinking that the rock I collected a couple of weeks ago from the same parent body but 40 miles away from the place I visited before would be the same. This rock is a beautiful varied mass of rose pink and white crystals. It is very high in silica and surprisingly free from impurities.

The colours it gives in the wood kiln can be seen best in this image of one of my disc forms. The pure, high silica, low iron, high potassium feldspar rock gives a very viscous melt, full of tiny bubbles, giving a smoky quality to the pale blue grey glaze. Where it gets a lot of heat the glaze rapidly fluxes becoming a glassy transparent of striking vivid blues. It is one of my very favourite rocks that I have found on my travels.

 

 

As soon as I saw the new rock I could see that it looked very different and has obviously crystallised out in quite a different manner. It was macrocrystalline, which means large crystals, and therefore slower cooling deeper within the earth's crust. The pink is there in the large feldspar crystals and in some of the ground mass surrounding them, but the main difference is in the grey sparkly crystals that are so abundant. These are flat plate like glittering crystals of mica and are the most variable of all the components of granite. They contain iron and sodium or potassium but also other minerals such as magnesium, manganese and possibly things like chrome and titanium.

These 'impurities' turn the pale blue colour into something else, depending on what is actually in there. More iron, and manganese give deepening greens and titanium is the kryptonite to superman's blue. As you can see from these initial tests the colours are much darker and very definitely green. The rock is much more fusible (easy to melt) and so produce quite clear runny glazes. 

I have about 4 initial tests that I do on a new rock, mostly progressive additions of one or two extra ingredients. Occasionally, when the sun is shining on me,  I find something stunning right here at this early stage but, as in this case, mostly a lot of extra work is needed. It's easy to get a rock to melt, but often quite hard to find that exact balance of additions that will coax its most beautiful colours out and transform it nto something sublime.

 

 

Winter in the Cumbrian Mountains

What better way to start off the new year and shake off that post-Christmas torpor than a few days walking in the Cumbrian National Park? The previous week’s snow held off, as did the rain. The barmaid in the pub I stayed in told me that the area had been unusually lacking in rain, however the moss covering absolutely everything was as thick, bright and moist as ever, and water seemed to be draining into every gully and dip in the landscape.

It was cold  with low sweeping clouds but once I got into the higher ground of the craggy glaciated valleys, where sheer rock faces protrude through the thining soil, towering above enormous scree slopes, I scarcely noticed. It is a beautiful an elemental place, carved out of an enormously complex variety of volcanic rocks, formed when the landmass of England and Wales collided with and joined that of Scotland.

Walking these lonely paths I found lumps of ‘frothy’ lava, huge slabs of laminated tuffs made from layers of compacted volcanic ash and huge ragged seams of pure white quartz. The brook and bridge in this image have become a tourist attraction after appearing in the ‘fishing with a shotgun’ scene in Withnail and I. The bridge itself is made from slabs of nearby limestone and is now hung with thousands of tiny white stalactites.

As I wound down this smaller valley I was approaching the edge of the National Park. It is hard to get all the permissions necessary to collect rocks from Parks as they are, rightly, protected areas. I had already secured the permission needed to collect from the site that I was heading to, which had been pretty easy, but the main reason for my interest in this spot was its geological interest. I had previously collected a similar rock from a site on the other side of the Park, a place over 40 miles drive away. Here, making up a small peak on one side of the end of this valley, is apparently the same rock. The two outcrops being exposed peaks of an absolutely enormous underground batholith that stretches the whole way beneath the mountains and lakes of Cumbria.

And here it is. Pink granite. But it doesn’t look the same as the rocks I collected from the other exposure. The pink feldspar crystals are much bigger and the crystalline ground mass surrounding them appears much darker with mica. One of the striking things about the other rock is the pale smoky blues and whites I can coax out of the other rock in my wood kiln, as it is so low in iron and manganese and other impurities commonly found in mica. But, as with books, I have learnt never to judge a rock by its colour/cover, and am very interested to see how this new version of geologically-the-same rock responds in my tests.