EDTA crystals, light micrograph
EDTA crystals. Polarised light micrograph of a section through ethylenediaminetetraacetic acid (EDTA) crystals. EDTA is used primarily for its effectiveness at binding metal ions (chelating). After being bound by EDTA, metal ions remain in solution but exhibit distinctly diminished reactivity. In industry it has a variety of uses, including for dissolving limescale and preventing metal ion impurities from modifying the colours of dyed products. In medicine EDTA is used to treat heavy metal poisoning through chelation therapy, where it is used to bind metal ions in the body. Magnification: x100, when printed 10 centimetres wide.
© MAREK MIS/SCIENCE PHOTO LIBRARY
Atomic structure, computer artwork. Schematic representation of the structure of the atom. At the centre of the model is the nucleus, made up of a tightly packed cluster of protons and neutrons. In this classical model, the nucleus is orbited by electrons with defined orbits. Modern quantum physics has shown, however, that is impossible to locate the exact position of electrons around the nucleus.
© DAVID NICHOLLS/SCIENCE PHOTO LIBRARY
Geode in thin section
Geode in thin section, close-up, viewed in transmitted polarised light. A geode forms when silica (SiO2) precipitates from liquid onto the inside surface of an empty pocket in a host rock. The outer layers are variegated forms of chalcedony (amorphous or non-crystalline silica), with the layers becoming more crystalline towards the centre. Here, a core of quartz (the crystalline form of silica) can be seen. The banded arrangement of crystals are a result of changes in pressure, temperature, and mineral content occurring during the formation process. Magnification: x3.8 when printed 10 centimetres wide.
© DIRK WIERSMA/SCIENCE PHOTO LIBRARY