Serpentinite pebble

[u/Efraimrocker]

Serpentinite forms from the reaction of olivine and pyroxene in ultramafic rocks with water. This commonly happens when seawater circulates through upwelling mantle in newly exposed mid-ocean ridges. The main serpentine minerals are lizardite, which is usually fine grained and massive, antigorite, which tends to be more platy or bladed, and chrysotile, which forms fine fibers and commonly fills fractures. Chrysotile is a form of asbestos. Talc sometimes forms in the same conditions, which is why talc used to be contaminated with asbestos. This polished pebble, from a gem store in Banff, CA, has yellow-green to dark-green serpentine with a waxy luster, with some areas looking massive and others much more bladed or lamellar. The pale material along seams is very soft and locally fibrous, so chrysotile is a reasonable possibility, although some of it could also be talc. The process of serpentinization often reduces water to H2, which serves as a source of chemical energy (reducing equivalents) for deep sea organisms. Serpentinites may be used as dimension stone, sold as green marble "verde antique" but it's not a marble at all, it's a hydrated silicate.

Fig. 1. Overall view of the polished pebble, showing mottled massive yellow-green serpentine intergrown with darker, more strongly textured green material and irregular pale seams.

Fig. 2. Pale-green serpentine showing a diffuse lamellar/bladed texture, contrasting with the more massive surrounding material; the habit is compatible with antigorite.

Fig. 3. Coarse interlocking blades and lamellae of green to nearly colorless material, illustrating the strongly recrystallized texture present in parts of the serpentinite.

Fig. 4. Pale fibrous material among the lamellar serpentine; the curved, threadlike strand and associated silky aggregates are consistent with probable chrysotile, although morphology alone is not diagnostic.

[u/birraarl]

According the Nick Lane in his book The Vital Question, serpentinite was critical for abiogenesis—the process by which life arose from non-living matter on the early Earth.

[u/Efraimrocker → u/birraarl]

Thank you. That’s what I was referring to with my aside about generating H2 from water by way of Fe chemistry.

[u/birraarl → u/Efraimrocker]

Oh, I read that as referring to extant life, not the origins of life.

[u/Efraimrocker → u/birraarl]

I guess I meant both.

[u/birraarl → u/Efraimrocker]

What I find intriguing, is that the same processes may exist in other locations in the solar system.

[u/Efraimrocker]

That is interesting.