A pretty rock I want to know more about

I have a pretty rock I want to know more about.



The purple looking one... The other three are normal coloration for this area (or orange sandstone) and I pick up a lot of them. Never seen one with purple in it though!

This area (SW Missouri) was once part of a shallow sea, and sometimes the grey rocks look like marble, intricately patterned, or have fossils in them!  But purple...

What would make it purple? Is it like what makes amethyst purple? Is it sea creatures? Puzzling rock to pick up!!  I like it.

I like your post Pearl.

Which one is the purple one?

I don't see amethyst in any of them ...

A quick google offered this as a starting point...

Rocks can be purple due to the presence of impurities like iron, which causes amethyst in quartz to turn violet, or iron in minerals like hematite and limonite. Other minerals that cause purple coloration include fluorite, sodalite, spodumene, and even biological deposits like coralline algae in marine environments. The specific mineral and its chemical state determine the exact shade and intensity of the purple.

Common Causes of Purple Coloration

Iron (in quartz):
The most common purple mineral in rocks is amethyst, a variety of quartz that gets its color from iron impurities within the silicon-oxygen crystal structure.

Iron (in other minerals):
Ferric iron (Fe+3) is responsible for many red, yellow, and purple hues, often found in minerals like hematite and limonite.

Other Elements:

- Manganese: Can produce pink crystals and is also a component in some manganese oxides that create purple coloration.
- Magnesium: Can also contribute to color, as seen in some magnesium-rich rocks.

Porphyry:
While not inherently purple, some types of porphyry can have a striking purple appearance and were historically used to symbolize power and royalty.

How the Color Develops

Impurities:
Elements like iron or manganese enter the crystal lattice of a mineral, replacing some of the original atoms and absorbing certain wavelengths of light to produce color.
Radiation:
Exposure to radiation can restore iron to a more typical chemical state, enhancing the purple color of amethyst.
Organic Matter:
In some cases, partially decayed organic matter, which can have purple hues, can contribute to the color of sedimentary rocks.

{quote=burra maluca] biological deposits like coralline algae in marine environments These rocks are all sediment off a dried up sea floor that compressed and turned to rock. Organic creatures might well be part of it, just not common.  
Cool! Thank you!!
:D

Looks like chert, common in sedimentary rocks. Chert is primarily  composed of a type of quartz.

Does it scratch glass?

If yes, could be quartz (and therefore chert)

If no, something softer, like dolomite or limestone is possible.

Either way, the purple color could be a result of iron or some other metal oxide, as mentioned by Burra. Doesn't look like fluorite, spodumene or the other exotic minerals. These are not found in Missouri.

But.....

Google says the state gemstone of Missouri is mozarkite! A colorful variety of chert/flint/jasper. Can be polished real pretty, makes good arrowheads, found west of Lake of the Ozarks.

I think that is the answer.

B Beeson: Oooh!  I think you win!
The gray rocks around here make excellent arrowheads, yes. Chert, I believe.
Orange limestone is all over around here, I know that when I see it.

Mozarkite is probably it. I saw an image online of that color on almost a whole rock, not just in ribbons like mine.
Cool! It has a name!
Thank you!! :D

According to some sources that might be called Chevron Amethyst.

Not the amethyst found in geodes that I am familiar with.

Google said, Chevron Amethyst, also known as banded or dogtooth amethyst, forms when layers of amethyst combine with white quartz in a naturally occurring V-shaped or zigzag pattern.

Anne Miller wrote:According to some sources that might be called Chevron Amethyst.

I wish it was! Those are lovely!
It's a Missouri ditch rock, and the Chevron Amethyst is only found in India, Russia, and and Brazil.

Pearl Sutton wrote:

Anne Miller wrote:According to some sources that might be called Chevron Amethyst.

I wish it was! Those are lovely!
It's a Missouri ditch rock, and the Chevron Amethyst is only found in India, Russia, and and Brazil.

Google says, Other notable sources include parts of the United States, Mexico, and Uruguay. The formation process involves silica-rich solutions filling cavities in rocks, leading to alternating layers of amethyst and white quartz in a characteristic V-shaped pattern

If you have any strong-ish acid around, a few drops on a questionable sedimentary rock will help ID limestone (or marble, if it's metamorphic), from sandstone, chert, and other rocks. Calcareous rocks (rocks with calcium carbonate) will bubble.

I often find chert to feel slightly waxy, and it breaks unevenly with sharp, angular bits.  I like the texture in my hand. It's hard, like quartz, so will scratch glass, and is opaque.

Assuming it IS chert, it has the same chemical formula as quartz - SiO2- the main difference is that it (usually) forms in a sedimentary rock , under lower temperatures/pressures so doesn't form big, arranged crystals like quartz.

I would guess that the purpling is likely due to the same process that forms amethyst from regular quartz - iron impurities, and a touch of radiation.

Edit - i often find quartz that has been touched by a bit of radiation, which damages the bonds in the crystals, (called smokey quartz in extreme examples) becomes greyer and a bit more translucent than a lump of common, not gem quality quartz but i don't see that in any quick reference sources i can find!

wow, mozarkite tumbles up beautifully!!
i used to be really into rocks and minerals as a kid, and managed to let it slide as my interests moved elsewhere. maybe it's time to get back into it!
https://rocktumbler.com/rough/mozarkite/

Tereza Okava wrote:wow, mozarkite tumbles up beautifully!!
i used to be really into rocks and minerals as a kid, and managed to let it slide as my interests moved elsewhere. maybe it's time to get back into it!
https://rocktumbler.com/rough/mozarkite/

Lots of pretty rocks around here. Now you make me wonder if I moved my rock tumbler or not., a lot of things didn't make the cut when I packed up multiple houses.. Hmm...

Edit, I just checked, it's on the packing list, but I'm not real sure where that box is. Hmm...

The first pic I posted of that rock (which has come into the house to be a domesticated rock!) was when I had first hosed it off. Looking at it now, there's a side that looks more dramatic, in this light it looks more maroon than reddish purple, could just be the LED bulb in this light.

chert.  Probably came out of a limestone.  The rock cracks or does solution cavities and the quartz silica rock is slowly deposited/concentrate by solution inside the limestone to form silica inside limestone or dolomite.  Cherts and flints are all silica.  generally cherts are lighter and flints are darker.  But they have slightly different crystal structures and it takes a true expert to tell them apart. Agates, Jasper, etc are forms of the chert/flint determined by color patterns and crystal structures.  And the naming gets more complicated.  In my area we have moss agate that has a dark dendritic pattern in the lighter agate.  But there is a form of moss agate specific to a single hill called spanish point agate that the dendritic pattern looks like a forest with a particular banding pattern in colors look like sky.



Way back as a teenager I spent lots of time trying to make arrow heads with no success.  Learned just a year ago at a class, at the museum, that most cherts need to be heat treated before they will flake right.  Apparently there is a real art to getting them to the right temperature and it varies because of their trace mineral content making it harder still

Burra Maluca wrote:Common Causes of Purple Coloration

Iron (in quartz):
The most common purple mineral in rocks is amethyst, a variety of quartz that gets its color from iron impurities within the silicon-oxygen crystal structure.

Iron (in other minerals):
Ferric iron (Fe+3) is responsible for many red, yellow, and purple hues, often found in minerals like hematite and limonite.

Just last night I watched this SciShow video about how amethysts get their purple hue:



They mention that it was recently discovered that amethyst is quartz that is colored purple by water dripping through iron-rich volcanic rock (often at pretty low tempurature). It is also naturally radioactive, which ionizes the iron which charge atoms which reflect emit purple light.

Amethyst is my birthstone, so when my first husband and I found this loose stone, he bought it for me, for my birthday. It was huge, and an odd cut, so they'd heavily discounted it, knowing it would be difficult to have set. For years, it sat in my jewelry box, because it was going to cost more for the setting, than it did for the stone - by about 5x. We had always agreed, before we even had kids, that it would eventually go to our oldest daughter, but I wanted it set, first.

Then, on a vacation in Gatlinburg, Tennessee, with my 2nd husband (probably 10 - 12yrs after buying the stone), we found this wonderful jewelry artist who wrapped stones! After I sent pictures, we settled on a price - that was only about 1/8 the cost of the stone, in 14k gold. This photo is zoomed in to my daughter wearing it, but she's not fond of sharing her face, online, so... I wish it were clearer. But, she wore it for her wedding.

I always felt that if I had an aura, it would be purple.

And if that aura could be represented by a stone, it would be amethyst.

A year or so after I lost my husband I was in a very strange place mentally - broken, but healing. Sort of. And very dependent on my new partner to hold me together.

I treated myself to a pack of rough amethysts, purchased online, in the hope that one of them might symbolise how I felt. And this one fit the bill perfectly!



Uncut, unpolished, falling apart at the seams somewhat. But held together by some copper stripped out of an offcut of electrical cable by my new partner, which might at first glance might look like a cage but actually keeps me from falling apart completely and allows me to face the world and shine as best I can.

It somehow captures my essence completely. Plus as it was a pack of five, he also made one up for his sister and one for his niece and there are still two smaller bits around somewhere, just in case we find a good way to use them.

Rock Hound who discovered fossils at @ 5 yrs here, Museum Junky, 3 yrs. pro "Exhibitionist" (fa true dat!) At effin Harvard's Agassiz Museum of Comparative Zoology.
'Nuff bragging, Did anybody ever notice that fotos of geeky stuff often include familiar coins? That's not for curiousity, it's to show scale. That helps ID a bit, size matters , (I've been told) The lithology of an area is often easy to find out: Volcanic/plutonic (granitic) or sedimentary: usually softer, & fossiliferous (even if microscopic) Here in Oregon the basic pattern is young sedimentary on the coast with some volcanics to furnish some good rocks to heat up for yr. traditional Clam Bake. The Cascades are mostly volcanic, and have some Copper in old volcanic pipes, and fossils like petrified wood from trees that were snuffed by Volcanic eruptions (means lots of free silica to replace the carbon; the volcanics and metal ores color the wood. Eastern Oregon is Obsidian is commonly Black or Brick red, sometimes with blooms of white microcrystals. So the pretty rock: Whereja find it? (what sort of place? Creek. Beach, Quarry , any mines around?  Do you have any resources around?  Geeks, Geology Depts. in Universities or museums? But warning, the Rockhound Bug bite can leave a lifetime itch. But poking around, do be sensitive to archaeology, whether in a river gravel or a traditional Obsidian Quarry.
I got my first multi-speed bike to get to quarries  (NW Ohio, limestone, with pyrite (fools gold) fossil brachiopods (little 'winged' seashells) and Trilobites. And also Celestite (Strontium Carbonate) that under a black light showed rose-pink, And the crystal pockets were big enough I could have crawled in. Why the company ever neglected to chuck us Junior HS rockhounds off their dangerous quarry is a mystery to me. So: does this give you any ideas on how the ID of that pretty rock can be narrowed down? Any library has geology books, any University has at least a geology dept. and maybe a museum. Maybe there's a rockhound club. I want to see you massively infected by the rockhound bug!

Rick Valley wrote: I want to see you massively infected by the rockhound bug!

You are about 50 years too late. I have been a rock person all my life. My parents and grandparents too.
This was in Southwest Missouri, left behind when a pile of dirt dug from about 5 feet down was removed. It looks very much like the rest of the rocks I like, except for the purple stuff.
The local rocks are sediment off a dried up sea floor that compressed and turned to rock.
Scale on  that pic is... from the two farthest apart points it's 7 inches across.

Do you have any clues? is the beautiful purple amethyst (quartz) a silica rock
Fluorite is another possibility, which is a carbonate rock if I remember right, much softer than quartz: so quartz will scratch fluorite but not vice-versa. If you're going to a rave or such, Fluorite will fluoresce under blacklite. All I have to go on is color and transparency