Just recently I went with a group on a rockhounding excursion to find...
Geodes! With baited breath, we battered through a collected handful of potentially crystaline rock shells. With a crack, the rock splintered asunder!
Sparkly, secretive and magical, this rock forms near ancient riverbeds and lavaflows. A hard shell forms around a pocket of air. Over time, crystals grow in that space.
Our second success was somehow full of water? Perhaps some leaked in through a crack. There’s a blue, riverish tint to this stone, which I find fitting C:
For those wondering, “what does the water from inside a geode taste like?” never fear. We cracked the geode and passed it around. Then a member of our party immediately licked it
Turns out the answer is “bad.”
We had great luck! Once you identify the light, circular, lumpy exterior, it’s easier than you’d think to identify a geode. In the Dugaway Geode Beds, quartz is so abundant that you’re likely to find something that glimmers without even cracking a stone
The bluish tint might make this celestite or angelite, I’m not sure which. And below, a troll tooth.
At the location, there was also a fair amount of this reddish stone- probably not a jasper, but I couldn’t help but take some home to test :>
Oh guys. GUESS WHAT!
OOIDS!!!! Those whitish circles clumped together on the inside are called ooids, a darn fun word to say that literally means “egg shaped.” Little balls of calcite precipitate out of shallow, calcium-rich marine environments and accumulate into ooidic structures.
Aren’t they ADORABLE??? Egg shaped, my beloved
Thanks for listening! Can’t wait to tell you all about my next adventure. Alright, now, everybody gather up for the group photo. Say “ancient marine envrionment!”
You stroll through the sandy dunes of an island with Rick, lost in this world of solitude together.
a/n: This is based 100% on the exact same trip I went to a year ago, to a place called Andros Island, more specifically Joulter’s Cay. I walked through an endless expanse of sand and blue water that stretched for miles on end, searching for sand dollars and butterfly sea shells all alone while my group was off in the distance. At the beginning of this short fic is a picture I took of this beautiful land.
You stood amidst an endless expanse of bleached sand that stretched in every direction, forming meandering slopes that dipped into shallow pools of glittering water, crystalline in their visibility and devoid of all life. The horizon teased you with its limitless symmetry, a boundary where land and sea intermingled like brackish water, and as you deeply inhaled the salty air, you wondered how far you could walk before the Bahamas Banks plummeted into the depths of the oceanic trenches and swallowed you whole.
The sun burned hot in the cloudless sky overhead, but you were well prepared for its unyielding power, having covered yourself with sunscreen and a wide-brimmed hat at Rick’s behest. His long fingers entwined with yours as you walked side by side, smiling at your enthusiastic wonderment while you marveled at how deeply your feet sank into the damp sand.
“This — this sand is really special, you know,” Rick commented, dipping down briefly to scoop up a handful of grains in his palm. “If you look closely, y-y-you can see that it's shaped like little spheres! They’re called ooids — funny word, huh?”
You peered into his proffered hand and did indeed catch sight of their unique appearance. “I don’t think I’ve ever seen sand like this. They look so perfectly circular and smooth.”
“That’s because of the way this particular island is structured. The limestone a-accumulating on the shores of the Bahamas is — i-is very old, and as erosion degrades the stone, bits of particles are released into the water. Limestone is made out of calcium carbonate, wh-which is found in abundance in the water. Over time, bits of limestone on the sea floor rolls with each passing wave, collecting the calcium carbonate like a snowball rolling down a snowy hill!"
“So there’s a lot of calcium carbonate in these waters?” you asked, dipping your foot into a little puddle as you walked by. “It’s not dangerous, is it?”
Rick chuckled and let the sand in his hand fall away between his fingers. “Not at all, mi corazón. It is, however, the reason why we aren’t seeing any fish or crabs in the water. Nothing survives here,” he finished with a hint of sadness.
You hummed in thought as you glanced into the basket at your side, the white shells of sand dollars twinkling up at you and clinking together with each step you took. “How did these sand dollars end up here?” you wondered, imagining them traversing through the ocean in search of a safe home, only to stumble upon a deadly environment that drained their life-force.
“Guess they got — g-got unlucky. Chose the wrong path in life.”
You glanced at Rick, unnerved by the sudden change in mood. He was turned away from you, staring off into the distance as the gentle breeze rustled his stringy hair.
“Hey,” you softly called out, bumping your joined hands against his hip to recapture his attention. Rick looked back at you in mild surprise, his eyebrows raised in question as you searched his pensive expression. “Are you okay?”
“I — I, oh, of course I am,” he replied, offering you a reassuring smile and lightly squeezing your hand. “It’s just, i-it really makes you think. These little moments, I mean.”
You remained silent in a bid to keep him speaking, leading him towards a colorful shell sticking out of nearby pearlescent water.
“I’ve been to so many different worlds, seen so — so many different t-types of living organisms, a-a-all trying their best to survive. It just —“ Rick bit his lip, furrowing his brow. “— i-it gets a little sad, seeing them … well, not make it sometimes. And they didn’t know that their choices would have bad consequences. They just went for it, and — and fate handled the rest.”
Your hand gently unfurled from Rick’s grip as you bent down to the seashell, plucking it out of the sand and running a thumb over it to remove any stray bits of grain. You held the shell between the tips of your fingers for Rick to see, admiring its butterfly-like shape and the alternating stripes of yellow and pink along the outer surface, bisected by horizontal white lines.
“All things come to an end,” you said, smiling softly at the seashell. “It doesn’t mean that life never happened to begin with. We all experience the brief gift of life, regardless of how short that may be. And look — “ You twirled the shell and lifted your basket to show him the sand dollars. “We leave behind such beautiful memories.”
A shimmer of wetness gathered at the corner of Rick’s eyes, but neither of you mentioned it. He gave you a shaky smile and placed his hands on your hips, leaning down as you kissed the tip of his nose. “I was being silly, w-wasn’t I?”
“Honey, you of all people have the right to a minor existential crisis every now and then.”
“G-gosh, that’s — I didn’t mean to be that depressing…”
“Nonsense,” you firmly replied, swooping in to press a quick kiss to his lips. “We’re in the Bahamas, Rick. There’s nothing you could say or do to ruin my incredible mood.”
He nodded, seemingly appeased by your reassurances.
You promptly decided to switch the subject. Your scientific curiosity had not been sated just yet — the pretty sea shell was still waiting for identification by your dear scientist, and so you brought it into view once more, laying the shell onto the palm of your hand as Rick got a closer look at it.
“What kind of seashell is this?” you asked.
“I … I don’t know, actually.” He laughed lightly, running a finger along its smooth surface. “I don’t get to say that very often, do I?”
You joined him in his merriment, twining your hand with his once more as you gently placed the sea shell into your basket of sand dollars. “Sometimes, it feels freeing to not know.”
Rick met your pointed look and smiled crookedly. “Even if the f-future is grim?”
“That, my love — “ You stood up on your tiptoes, sinking into the sand as you quickly kissed his cheek. “ — is life!”
Upon first glance, these small, rounded grains look like the white sand you would expect to find on a tropical beach. However, their formation is quite unique. While sand forms from the breakdown of rock into increasingly smaller pieces, ooids grow over time. Ooids are accretionary mineral bodies formed of calcium or aragonite. They most commonly form in warm, shallow marine environments where the water is supersaturated with calcium carbonate. Areas with high energy due to wave or tidal action suspend small sand or shell particles in the water column. These particles serve as nucleation sites and calcium or aragonite precipitates out of the water forming concentric layers of mineralization. Periods of mineral growth are interrupted when the ooid falls out of the water column into the sediment below. This intermittent growth is evidenced by their characteristic layered or ‘tree-ring’ cross section. In the thin section photo below, the ooids’ layers evenly surround and mimic the shape of their respective nucleus. Ooids are generally less than 1 mm, but can grow up to 2 mm in diameter. Higher energy environments can support heavier particles in the water column, and this allows for larger ooids to form. Two well known locations for modern ooid formation are the Persian Gulf and the Gulf of Mexico.
The name ooid comes from the ancient greek word for ‘egg shaped’ as they bear a resemblance to fish eggs.
Our oceans are actually “supersaturated” in carbonate minerals, including calcite, aragonite, and dolomite. If you go back to chemistry class, that means that the concentrations of calcium and carbonate (and magnesium for dolomite) are high enough that those minerals will spontaneously precipitate from the ocean if put in the right circumstances. However, those circumstances aren’t common on Earth. Carbonate minerals are “kinetically inhibited”. It is difficult for the oceans to nucleate the first crystals of carbonate minerals from dilute solutions such as ocean water. However, once a tiny crystal of carbonate has formed, it will grow spontaneously on that crystal, making any small crystal of carbonate progressively larger.
Some situations can trigger spontaneous carbonate formation. Lots of water evaporation, such as in a shallow and warm sea, will concentrate carbonate even more, making it so supersaturated that the minerals will precipitate regardless of any difficulty nucleating crystals. About 545 million years ago, life also figured out that if it gave carbonate minerals a surface where they could nucleate easily, then the natural chemistry of the ocean would grow a hard, solid surface with little effort. This discovery marks the appearance of life with hard parts in the fossil record which we recognize as the start of the Cambrian period.
These rocks from Jurassic aged limestones in the Czech Republic are another consequence of this ocean chemistry. These are ooids viewed under a microscope, magnified 30x in the first image and 200x in the second. The whole first image is just under 1 inch across.
These start off as a tiny piece of calcium carbonate, maybe even a broken shell. As they are rolled around in the waves, calcite precipitates on the surface. The minerals won’t form new crystals on their own, but previously formed grains rolling around in supersaturated water can gradually turn into round, coarse sand sized particles of calcite. When they are polished through the center and viewed under microscope, they show off concentric layers grown one after another around the center.
-JBB
Image credit: Petr Hykš https://flic.kr/p/U2Kp3q https://flic.kr/p/UBNcuk
While these dark gray spherical clasts could be mistaken for some type of fossil, they’re actually ooids, which are chemically precipitated sedimentary grains.
Ooids form around a nucleus of a mineral grain or shell fragment. Concentric layers composed of calcium carbonate precipitate out and progressively coat the nucleus, forming a pattern almost like tree rings. In the bottom right photo, you can clearly see the center nucleus and the individual surrounding concentric layers that compose the ooid.
Generally, ooids form in shallow wave-agitated water. These higher-energy marine settings allow for accretion to occur on all sides of the grain and for their well-polished appearance. However, ooids are also known to form in non-marine settings, such as the Great Salt Lake.
Grains that are less than 2 mm in diameter are termed ooids, while those larger than 2 mm are termed pisoids. Accordingly, ooids cemented together form the sedimentary rock oolite, and pisoids form the rock pisolite.
Specimens of unknown age from Banff, Alberta, Canada
