This is a slightly expanded version of my letter “Y” contribution to the current weekly Alphabetical Series in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. In the 2021 version of this Series I posted “Y is for Yellow Beach Stone from Kaikoura Coast”.
Y is for YesterYear’s Yellows at Year End (A New Year’s Eve Post)
I found this intriguing stone of many shades of yellow on Gemstone Beach on 27 March this year (2025). It’s probably mainly quartz, with some minerals providing the colours, many of which seem to be at the orange end of yellow. Looking back from the last week in 2025 through my finds this year, and even further back in time, I am surprised how many yellows there are. And a lot of them are visually very interesting. Keep in mind that colour perception is subjective – I suspect we all see colours slightly differently. I know that I sometimes disagree with fellow fossickers over the colour of some stones – what seems orange to me can seem pink to them. And I sometimes can’t decide whether a stone has crossed the colour boundary from yellow to orange, or from yellow to brown.
After some research in my geology texts and online, it seems that the yellow in the kind of beach stones I find is likely to be mainly caused by iron minerals, especially hydrated iron oxides like limonite and goethite, formed from the weathering and oxidation of iron-bearing minerals. The sources I consulted point out that the same mineral can cause different colours depending on a number of factors. So, for example, the presence of chromium causes red ruby as well as green emerald. Colour arises from the absorption or refraction of light, and as few as three or four atoms per million can absorb enough of the visible light spectrum to give colour to a stone (information provided by R.L. Bonewitz, 2015, “Rocks and Minerals: The Definitive Visual Guide”, page 92). If you look at the Gemstone Beach find featured at the top of this Post, it has a lot of variations of colour in it, most of them yellow/oranges but also brown and green. All of these could be caused by different concentrations of the same mineral (likely to be a hydrated iron oxide). The colour yellow itself it not straightforward. There are many variations and hues, some of them bordering on other colours (especially orange, brown and green). A sense of this diversity of yellows can be seen in the diagrams below.
Wikipedia has a long and interesting entry about the colour yellow, its history, and its various meanings: Yellow ochre pigment was one of the first colours used in art; because of its high visibility, yellow is often used for traffic signs and to warn of the need for caution; a yellow card is used in some sports as a last warning; because gold is yellow, one of its associations is with wealth; but yellow is also symbolic of cowardice. Below are 11 more stones showing the yellow variations I have noticed in my finds over recent years: the lemon yellow sometimes seen in Kaikoura Coast limestones; the creams of Kakanui’s fossiliferous limestones; the orange-yellow iron-stained quartz stones of Kai Iwi Beach; the bright yellows in Gemstone Beach hydrogrossular garnets; the yellow-browns of Kakanui’s bryozoan fossil stones; and the yellow-oranges of Kakanui’s quartzites (see this Post for an idea of the range of colours in Kakanui’s quartzites).
The next Post in this Series is “Z is for Zeolite”. An Index for this Alphabetical Series is here.
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