083019b

Calcite cement (pale pink) dissolving feldspar and quartz in a very fine sandstone, Rodessa Formation, Citronelle oil Field, Alabama, about 11,000 feet below the surface, thin section, scale bar 100 micrometers, crossed polarizers.

041919

Two examples of dedolomite (dolomite that has been dissolved) from the Jurassic Smackover Formation in Alabama. In the first image, some dolomite crystals are hollow. Blue indicates open pore space. In the second image, hollow dolomite crystals have been filled by calcite cement (pink, stained by Alizarin red S). These samples come from rocks buried several miles below the surface. Thin section photomicrographs, 1 mm across.

033119

Dolomite (gray and white); this rock was once very porous, but all the pore space has been filled with calcite cement (stained pink with Alizarin red S), note partial replacement of rhombic dolomite crystals with calcite; dolostone of Knox Group, Mississippi, thin-section photomicrograph.

010518c

Burrows on Mars? http://www.leonarddavid.com/curiosity-mars-rover-investigates-eye-catching-odd-features/?utm_source=twitter&utm_medium=social#?utm_source=twitter&utm_medium=social&utm_campaign=2016twitterdlvrit

We already know Mars has gravel that was almost certainly deposited by flowing water, can critters be far behind?

 I should say that an origin of these marks by burrowing is highly unlikely. Chemically fragile crystals (such as those of evaporite minerals) are commonly dissolved and replaced by sand or other materials. This is a common process, and doesn't require organisms to produce it.


It would be astounding and wonderful to find proof that multicellular life has existed on Mars, but it is far more likely that we will find proof that minerals have been dissolved and replaced.

A very old skeleton

What used to be a hale and healthy feldspar sand grain is now hardly a shadow of its former self. Blue is open space. Note the scale.

Something rotten

A close-up of sandstone, showing a grain of plagioclase feldspar (blue-gray) having been partially dissolved, and the holes filled in with calcite (pink)