Fig 1.
A) Photograph of a garnet crystal with distinct tubular structures. B) Microphotograph of network of tubular structures originating at the mineral surface and stretching into the garnet relatively localized to the margin of the garnet. C) Tomographic reconstruction (isosurface rendering) of a garnet crystal with network of tubular structures originating at the mineral surface and stretching inwards into the crystal interior. The interior of the crystal are made black to make the tubular structures more visible. Legend: ms, mineral surface.
Fig 2.
Images A-B: CT almandines; C-F: KW pyropes; G-H: CT pyropes. A) Tomographic reconstruction (isosurface rendering) of a garnet with tubular structures originating at the surface. The bases of the tunnels are broad and have distinct hexagonal or rectangular cross sections but tapering off and become more rounded toward the tips. B) Tomographic reconstruction (volumetric rendering) showing the hexagonal cross section of multiple tubular structures. C) An orthoslice of a tomographic reconstruction showing the cross-sectional hexagons or rectangles of the tunnels. D) SEM image of a four-angled polygonal entrance hole. E) SEM image of a six-angled polygonal entrance hole that is filled. F) SEM image of a tubular structure that tapers off further into the mineral. Note how the tunnel have a polygonal shape at the mineral surface but further in gets more circular as it tapers off. G) Microphotograph of a tubular structure that tapers off and also starts with a polygonal shape at the mineral surface but gets more circular as it penetrates further into the mineral and tapers off. H) Microphotograph of tubular structures that tapers off. The branching of the tunnels results in offspring tunnels with less diameter than the originating tunnel.
Fig 3.
Images A-B: BR pyropes; C-E: NB pyropes. A) Tomographic reconstruction (isosurface rendering) showing straight and strictly parallel tunnels entering from three different mineral surfaces forming almost perfect rows. Arrows mark the three different mineral surfaces. White arrows mark external mineral surfaces and the black arrow marks the internal mineral surface. B) Tomographic reconstruction (isosurface rendering) of tunnels, although parallel, but not lined up and more irregularly scattered. C) Microphotograph of parallel tunnels with a seemingly coordinated curvature of the distal parts of each tunnel. Arrow marks the curvature. D) Microphotograph of a few parallel tunnels with a common curvature. E) Tomographic reconstruction (isosurface rendering) of palisades within a crystal, where internally parallel tunnels in each set make distinctive angles to co-occurring sets projecting in other directions. See arrows.
Fig 4.
A) Tomographic reconstruction (isosurface rendering) of a network of tubular structures forming a complex network with frequent branching and anastomoses between branches. B) Tomographic reconstruction (isosurface rendering) of a garnet showing tubular structures originating at the mineral surfaces penetrating into the mineral. The network is characterized by branching but also anastomosis between branches. An arc-shaped tubular structure is also seen. Legend: br, branching; sb, serial branching; as, anastomosis; arc, arc-shaped tubular structure. C) Microphotograph of part of a garnet with straight, parallel tunnels that reach from one side of the garnet to the opposite side. D) Microphotograph of a tubular structure that contains a reddish filament-structure with precipitations on its surfaces. E) Microphotograph of tunnels with a reddish filamentous filling. F) Close-up microphotograph of the filamentous structure inside the tunnel in E.
Fig 5.
EDS data of the tunnel content.
Spec 1–4: CT garnets, spec 5–6: KW garnets and spec 7–8: BR garnets. All measurements have been done on freshly cracked garnets. Thus, the analysed tunnels were exposed only seconds before being introduced to the vacuum chamber of the ESEM system. All tunnel analyses are presented with data from reference spectrum of the garnet.
Fig 6.
ToF-SIMS and SEM images of two tunnel-containing regions in two different garnets; A-E: CT pyropes, and F-J: KW pyropes. A) Micrograph of first garnet. Green square indicates area of ToF-SIMS analysis. B) ToF-SIMS negative ion image overlay of SiO2- (red), CN- (green) and PO3- (blue). C) ToF-SIMS positive ion image overlay of Mg+ (red), Na+ (green) and K+ (blue). D) ToF-SIMS ion image of CN- (green in B) overlain a SEM image of the same area. White square in B-D) indicate area of SEM image close-up shown in E). F) Micrograph of second garnet. Green square indicates area of ToF-SIMS analysis. G) ToF-SIMS negative ion image overlay of SiO2- (red), and fatty acids (green, added m/z 241, 255, 269 and 283) and CN- (blue). H) ToF-SIMS positive ion image overlay of Mg+ (red), Na+ (green) and K+ (blue). I) ToF-SIMS ion image of fatty acids (green in B) overlaid a SEM image of the same area. White square in G-I indicate SEM image close-up shown in J).
Fig 7.
Negative ToF-SIMS spectra of freshly fractured surfaces of three different minerals: A, B, C) garnet, D, E, F) hematite, and G, H, I) quartz. Fatty acid peaks are found in spectrum of the garnet at m/z 241.17 (A, D, G), m/z 255.20 (B, E, H), and m/z 269.20 (C, F, I). All spectra were performed for 200s on 200x200 μm2.