This very attractive mineral can often look similar to crystals of quartz, the crystals are found in association with Zeolites which are a confusing group that I will be looking at in detail later. Crystals of Apophyllite ...
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nearly always occur as transparent or translucent perfectly formed crystals and are found in a variety of colours that originate from minute inclusions of Chlorite or Hematite and related elements, Apophyllite is of hydrothermal origin, forming in any cavities in basaltic or tufacious rocks of extrusive igneous origin and it is formed as a late stage mineral often occurring on top of other early stage crystallised minerals.
Apophyllite is technically referred to as a Hydrated Potassium Calcium Silicate with Hardness of 4.5 to 5 and it is therefore softer than Quartz. The commonest form is as beautiful quartz like crystals that have square elongated columns with sharp pointed terminations as opposed to the hexagonal columns of Quartz. This mineral also has a usually glassy appearance as seen in the pictures, the transparent crystals can be difficult to see clearly against pale backgrounds, one example illustrated is on a black Chalcedony base and therefore the clear crystals can be more easily seen. This mineral also forms cubic shaped lozenge like crystals as well as complex twinned forms.
This highly aesthetic mineral is unfortunately not often listed in many conventional books on minerals which seem to occasionally avoid all Zeolites and their associated minerals.
Frequently seen at Gem Fairs, Apophyllite forms as part of the tetragonal group of crystals; Vesuvianite is also part of this group and has similar elongated columns with a cubic cross section. The main columns often have a vitreous lustre and can also exhibit striated faces; the basal pinacoid often exhibits a distinctive pearly lustre as well. Most crystals have a pyramidal termination at one or both ends.
The most sort after colour variety is pale luminous green and lovely examples of this are found perched on contrasting brilliant white Stilbite sheaves from the only Apophyllite Mine in the Pushan Hills, Pune, Maharashtra, India. Other examples also come from the Poona area of India with flat terminated crystals from Ahmednegar. There are also fine crystals from nearby Shadin again in the Maharashtra region along with other examples from the nearby Nasik area all on the Deccan Plateau.
Some crystals exhibit a very curious zoned effect, caused by a distinct change in the levels of impurity as the crystals grow, probably linked to saturation levels in the circulating fluids. These crystals are also found in the same general area as the green crystals listed above but this time from Nasik.
Red and Chocolate crystals
Much admired are the very rare Magenta and Dark Brown coloured examples, the colour is due to microscopic inclusions of varieties of Hematite, Vanadenite, Proustite and Greenockite and the colour can vary depending upon the level of inclusions from very pale limonite to deep almost black Hematite. The very rare dark brown colour known as Chocolate Apophyllite comes from Jalgaon north east of Bombay.
World Wide Occurrences
As this mineral is of Hydrothermal origin it is found in relatively recent volcanic rocks in places such as Iceland, Greenland, Nova Scotia, the Faroe Islands, Italy and Brazil as well as lots of less well known Volcanic regions.
The Isle of Skye is very well known for its Zeolites and it is no surprise that the associated minerals are also found there. Very good but small crystals of Apophyllite are found at Moonen Bay on the Isle of Skye along with Chabazite and Heulandite.
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