All gem hunters in Yarrow Creek soon become familiar with the most abundant minerals to be found there. Quartz, as always, leads all the rest in quantity. Mostly it's waterworn, but the occasional near pristine crystal turns up.
Along with the quartz, orthoclase felspar is sometimes seen. No doubt, both the quartz and felspar are derived from veins in the granite, which outcrops in most places fossickers go.
Black spinel (pleonaste, blackjack), corundum (a high proportion of which is gem quality sapphire), zircon and pyrope garnet are found everywhere. Sometimes the vagaries of the currents during floods cause the zircon and garnet to be concentrated separately, though always with spinel and corundum.
The less common minerals,but still common enough to be found every visit or so, are enstatite and schorl tourmaline. Topaz is found once in a while, perhaps one or two pieces in a year of regular weekly outings. Once a blue specimen was found. Just once a pale specimen of ruby turned up in my sieve, and this has already been illustrated in the blog entry on pink sapphires.
Finally, there are the miscellaneous things that turn up, which, while not all one-offs, will bother most
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| Ilmenite |
fossickers trying to identify them. Ilmenite is reasonably common but not normally noticed. It occurs as cylindrical, metallic lumps, though why it is in this form I do not know .
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| carnelian 3cm across |
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| Silicified wood 11cm long |
I've seen the occasional piece of agate, though I failed to photograph one. The photo of the specimen of orange chalcedony (carnelian) is a one-off, as are the silicified wood and rutile. The chalcedony would be related to the silicification of wood trapped beneath the nearby basalt flows, though I would have expected them to be more abundant.
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| Rutile 2cm long |
The specimen of rutile is an unexpected find, mainly because I have never seen another. Such a vast amount of rutile has accumulated in heavy mineral deposits along our coasts that I would have expected more to turn up in creeks like Yarrow which drain in that direction.
Lastly, here is a specimen about which I know nothing. It was found amongst the sieve concentrates, so it's reasonably dense. It doesn't look like the rest of the corundum, which I thought it was initially. It remains a mystery mineral.
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| Unknown mineral |
Check my gem hunting
videos from around Glen Innes here . I also have playlists on Glen Innes, the Blue Mountains and New Zealand.
https://johnsbluemountainsblog.blogspot.com/2013/12/links-to-all-blog-entries-and-relevant.html
All Blue Mountains blogs and videos
All New England and other Geology blogs and videos
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| The mineral we all want to find: 16.8 carat blue sapphire |
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