“Mrs Purple” is a friend who has followed my stone collecting trips and sometimes indicated that she likes one of my purplish-coloured stones. She likes all things purple and I recently told her I would send her some polished purple stones. However, “purple” is not a straightforward colour when it comes to stones. This led me to take a closer look at the colour purple.
Only a tiny part of the electromagnetic radiation spectrum is visible to the human eye. Cosmic rays, x-rays, microwaves and radio waves, for example, are all invisible to us. Visible light is made up of a range of colours between red and violet. At school, I learned the sequence of the colours of the rainbow (which are the components of visible light) using the mnemonic ROY-G-BIV – Red, Orange, Yellow, Green, Blue, Indigo, Violet.
It was Isaac Newton in the 17th century who refracted sunlight through a prism to reveal the different wavelengths of visible light. The Blue-Indigo-Violet part of the spectrum is sometimes controversial as Indigo seems quite close to Blue. Some think that Newton wanted seven colours because of the traditional value put on the number seven (see medium.com). However, this Post is not about Indigo but about Purple, another name for Violet.
Traditionally, Purple is an equal mix of Blue and Red. However, Purple can also be viewed as a range of hues occurring between Blue and Red.
An added complication is that human perception of colour is not objective. We don’t all always see the same thing in the same way. We might be colour blind, for example. We also tend to see what we expect, based on our past experiences. Optical illusions demonstrate that what we see depends also on context, as in the following three colour illusions:
The human sense of sight is fallible, subject to tiredness and fading and such environmental conditions as light levels.
Now let’s turn our attention to stones. There are few purple stones, even fewer of which are the standard purple colour (though some variations of charoite and sugilite seem to be). Amethyst is a purple variety of quartz. According to mindat.com, it owes its colour mainly to gamma irradiation and the presence of iron – in fact, iron is the most common mineral to produce purple hues in rocks. Other minerals can have a purple effect. For example, purple sapphires have that colour due to traces of chromium present during formation – and they can range widely in hue.
I don’t come across beach stones of the standard purple colour in New Zealand. But there are a few that fall into some of these suggested 20 shades of purple.
In terms of the predominant colour of the “purple” stones I find on beaches, it is the darker hues like boysenberry, plum, sangria and mulberry that are more likely to crop up, for jaspers and quartzites, for example. But when one looks more closely at the veins within stones, where some mineral like iron has concentrated, then a greater range of hues emerge, including purple, violet, lavender and magenta.
As I noted above, human sight is subjective and fallible. What I see as purple may not be seen so by another. Light conditions affect how a stone looks. Photography adds another layer of complex variations and “distortions”. These should all be kept in mind when assessing the colour of a stone.
I sent 20 polished stones from three southern South Island beaches to Mrs Purple. They are among the “most purple” of the stones I have tumbled. Ten are from Gemstone Beach (Southland), six from Kakanui (North Otago) and four from Riverton (also in Southland). These are numbered in the three photos below.
This Post, Part One of a two-part Series, will look at the ten stones from Gemstone Beach. I had originally intended to describe each stone in terms of which “shade of purple” can be found in it. But I discovered that this was too difficult, moving between the shades and the stone, trying to distinguish the hues. I felt I ended up giving inaccurate attributions. So I will restrict myself to more simplistic observations, letting the photos of the stones largely speak for themselves. For each stone, a photo of each side is presented, along with a close-up from each side. Here are the first two stones from Gemstone Beach:
Most of Stone One is a mix of darker hues and small areas of lighter hues as well as white quartz crystals. There is an intense wavy band of what appears to me to be “magenta” in colour. Stone Two is a contrast to Stone One, being much lighter in colour overall, having hues that are much pinker. Stones Three and Four are different again:
Stone Three again has light to dark hued spots all mixed in together though they are much finer-grained than in Stone One. Stone Four is a dark reddish-purple hematite jasper (the gray hematite is an iron oxide). Stones Five and Six are the smallest of the 20 stones for Mrs Purple:
Stone Five, a small jasper, has some cream-coloured sections along with at least two different dark hues of purple and a more reddish band. Stone Six is amygdaloidal – a volcanic stone that has had small vesicles (holes) in it caused by gases, which were then filled by mainly (in this case) white material left behind as water has passed through over thousands of years. There are three darker shades of purple apparent as well. Stones Seven and Eight are just a little larger:
Stone Seven has an almost orange-purple through it, while Stone Eight has intense dark purple veins. Stones Nine and Ten are larger, with Stone Ten being the largest of the Gemstone Beach stones:
Stone Nine, with a clear silica vein, has a scattering of light purple throughout it. Stone Ten is predominantly a dark stone, with some thin veins of intense purple and some creamy-white patches.
Part Two of this Series (not yet available) looks at the remaining ten stones sent to Mrs Purple, from Kakanui and Riverton.
While writing this, I viewed a tv documentary on the New Zealand music band Six60, “Till the Lights Go Out”, and became aware of their song “Purple”:
“Purple” by Six60
I’ve been holding on to nothing
Reaching out to something
Waiting for someone like you
If only there was one thing
Some way of controlling
All these other things I do
Shock me girl electric blue
Standing while the wreck’s still true
And so we fall
And through it all
I’m left here with this purple heart of mine
Battle’s won
The war is done
And the sky is purple, purple, purple
Last night I was dreaming
Falling from the ceiling
Woke up just before the sound
And it got me thinking
Oh I got that feeling
We’d already hit the ground
Shock me girl electric blue
Standing while the wreck’s still true
And so we fall
And through it all
I’m left here with this purple heart of mine
Battle’s won
The war is done
And the sky is purple, purple, purple
I’m a keep shining
I’m a keep shining…
Ooley Dooley awesome