Parting Shot

The Oxford English Dictionary defines ‘vector’ as a quantity having direction as well as magnitude, and ‘scalar’ as a quantity having only magnitude, not direction. Much geological research starts with fieldwork, manifestly a vector activity. In Figure 1A, the geologists are exploring the intersection of a complex, 3-D body, the layered Klokken syenite, a 4 × 3 km igneous intrusion in the Gardar alkaline province of SW Greenland, with a mountainous 3-D land-surface. I described the unusual layering in Elements v10n1 (Parsons 2014). The igneous rocks were emplaced 1,166.3 ± 1.2 million years ago, and the 650 m of 3-D topography, which reveals the inner workings of the magma chamber, was carved by the advance and retreat of the mighty Greenland ice sheet in the last few thousand years. Only the age (a U–Pb age from baddelyite, ZrO2) is a scalar quantity.

In their doomed attempt to keep me near the cutting edge of technology, one of my sons recently bought me a grey cylinder that, when connected to an electricity supply, answers (literally) to the name of Alexa. She speaks BBC English with a mellow, alto voice and can, sometimes, answer my questions. Early in our relationship, to see how smart she really is, I asked her a question with three answers, ‘How far is it to Glencoe?’

I must explain the extension to my title. I wrote a Parting Shot with the title ‘Nooks and Crannies’ for Elements, 8 (2), 2012, in an issue on ‘Minerals, Microbes and Remediation’, devoted to nooks and crannies on weathered alkali feldspar surfaces. For international readers, I explained that (according to the Concise Oxford English Dictionary) a ‘nook’ is ‘a corner or recess; a secluded place’ and a ‘cranny’ is ‘a chink, a crevice, a crack’. The reactivity of complex mineral surfaces is a complicating factor in ‘reactive transport’, particularly near Earth’s surface. The present issue provides me with an opportunity to dust-off a few old micrographs, images of considerable beauty in themselves, to remind readers that minerals are not just chemical compounds. It also allows me to introduce an intriguing discovery of the last five years. Some, but not all, feldspars are extremely effective at nucleating ice in clouds, and this may be related to nooks and crannies, not just to chemistry.