Pics 1 and 2: two surfaces of a greenish crystalline rock, no real foliation. Pics 3,4: also faintly greenish. Found along trails in Wengen, an alpine village in the Jungfrau region.
Serpentinite is a rock composed of serpentine minerals formed when water reacts with olivine-rich ultramafic rocks (peridotite) at low to moderate temperatures (~100–400 °C). Olivine exists along a compositional spectrum between Mg-rich forsterite and Fe-rich fayalite. Mg-rich olivine reacts with water to form serpentine minerals and brucite (Mg(OH)₂), while Fe-bearing olivine can undergo oxidation reactions such as:
3Fe₂SiO₄ + 2H₂O → 2Fe₃O₄ + 3SiO₂ + 2H₂
In this process, iron is oxidized and water is reduced, generating hydrogen gas and releasing heat; serpentinization is therefore an exothermic reaction that can locally elevate temperatures and drive hydrothermal circulation even in the absence of active magmatism. Because it produces hydrogen and highly reducing conditions, serpentinization has been proposed as a potential energy source for prebiotic chemistry and early life.
There are three main serpentine minerals: lizardite, antigorite, and chrysotile. The first image shows massive serpentine (likely lizardite ± antigorite), while the second shows antigorite replacing elongated orthopyroxene crystals, preserving their original bladed texture—a feature known as “bastite.”
Chrysotile, not shown here, forms silky fibrous aggregates and is one form of asbestos. It commonly forms along fractures during serpentinization and may occur with talc under silica-rich conditions; its industrial use led to contamination issues in some talc deposits and associated health risks.
Does anyone have granulite facies metamorphic hand samples for sale?
This image illustrates a **fluid-driven metasomatic gradient in which relict garnet is progressively replaced by epidote and amphibole as fluid flux increases across the rock.
This image illustrates a fracture-hosted quartz vein acting as a fluid conduit from which channelized retrograde alteration propagates into the surrounding rock.
3. This image illustrates infiltrative dissolution–precipitation replacement of garnet by epidote along a fluid-accessible interface adjacent to a quartz vein.
4. This image illustrates incomplete, patchy replacement of garnet by epidote, preserving relict grain textures within a fluid-driven metasomatic front.
5.This image illustrates grain-scale dissolution–precipitation replacement, with epidote infiltrating and consuming relict garnet along microfractures and grain boundaries.
**6.**This image illustrates heterogeneous, permeability-controlled metasomatism in which epidote preferentially replaces host minerals along microfractures and porous pathways rather than uniformly across the rock.
Morton Gneiss is an Archean, high-grade metamorphic rock from southwestern Minnesota, with protoliths and metamorphic events dating back roughly 3.7 billion years. It represents deeply reworked continental crust that has undergone multiple episodes of deformation, metamorphism, and partial melting, producing a classic migmatitic gneiss. Its significance lies both in its antiquity—among the oldest exposed rocks in North America—and in its record of early crustal evolution, preserving evidence of repeated tectonothermal cycling on the early Earth. The characteristic banding and, in some specimens, dramatic swirling patterns reflect intense ductile deformation coupled with melt segregation under high temperature–pressure conditions in the deep crust.
Mineralogically, it is dominated by quartz and feldspar (both potassium feldspar and plagioclase), with variable amounts of mafic minerals such as biotite and hornblende forming darker domains. In your images, these phases appear as an interlocking, coarse-grained mosaic with irregular grain boundaries indicative of high-temperature recrystallization. Rather than strong, continuous banding, this specimen shows a more mottled distribution of felsic and mafic components, with only weak alignment of darker minerals—suggesting partial homogenization after melt formation. Local feldspar textures (cleavage faces and possible perthitic intergrowths) and quartz-rich zones reflect leucocratic melt segregation, while the darker patches represent more mafic residua, together producing the “mishmash” texture captured in the photos.