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I need help, what is this???


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The one you're holding in your hand looks like some sort of hard coral or perhaps a pertified sponge, but too me also looks like a type of bubbly volcanic rock, I think scoria, when I look it up, but I had remembered the name as tuft.  When organic material petrifies, the organic material gets replaced molecule by molecule with whatever material is around or seeping though and dissolved in the water.  I've seen pictures of a petrified snail that is made of fools gold, also the petrified wood from North East AZ can be made of Agate.  Too my untrained eye, besides the picture of the rock you're holding, the other material does not really look like a fossil, but during the petrification process, maybe it is a not so well persevered specimen as 4 meter said.

As a rule, I don't download videos from the forum in MP4 to watch, but will watch links to YouTube.  The downloads either fill my computer up, or for some reason tend not to work.

Edited by chrisski
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A close up look at the crystals would differentiate gypsum from silicate replacement minerals (fossils). A little vinegar might help although the results may be confusing. Hardness of the crystals would be a determining factor.

I would look at the crystals under a loupe and see if they matched the geometry of quartz or one of the soluble minerals. I would look very closely at the pattern the cavities made and ask myself if this was growing, melting or a solidified object. I would look at the structure or "grain" and ask myself if it was a result of a solid object solidified or the result of crystal growth or disintegration. And then I would poke a single well formed crystal with the point of a pin and see how hard it was. Solubles are very soft and powder up easily. Quartz and silicates are tough like little chunks of glass.

From the photos I would guess it is not an object solidified but a crystal growth. And from the grain I would say those crystals are bladelike (gypsum) and not needle like (quartz). The form and grain is one of growth and disintegration (like ice near splashing water) and not a solidified form. The red hues are indicative of gypsum as well (although fossilized material could also be that color). 

I assume the wall of the excavation in the photo is the earth you found it in. It is sedimentary and saline/clay soil. That is also indicative of a soluble mineral. Not so much fossilized coral.

So that is how I came to the conclusion in case that information helps.

Identify it by determining if it is a soft soluble like gypsum or a hard silicate like quartz. That is an easy task when you are holding the specimen. Not so easy from a photo. Crystal shape, hardness and solubility are the tests that you need to do to identify the mineral.

 

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I saw a demonstration in school about gypsum. A fellow was from the USG Corporation and he used the white sand from White Sands Monument and selenite crystals from nearby. 

The stuff would half dissolve in water that was almost freezing and then re-crystallize when the water boiled. After a few freeze/boil cycles all the sand was beautiful freshly formed crystals. He explained that is how the selenite roses formed in the winter when the freeze/thaw cycles stimulated growth.

He added a pinch of table salt and everything disappeared in nearly freezing water. And the evaporate made crystals like strings of yarn on a petri dish. It almost looked like a fungus stalk or something. Sodium salts make gypsum more soluble and magnifies crystal growth. So salt basins are the perfect environment.

Pretty amazing stuff. 

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