A report on the chemical and mineralogical analysis of samples’ solid inclusions.

A unique specimen of fossil resin originating from the Dipterocarpaceae tree family found in Miocene brown coal deposits in Jambi Province (Sumatra, Indonesia) was investigated via microscopic observations, microhardness testing and infrared and Raman spectroscopic methods. Its form is rare in nature, being an aggregate of three varieties of resin differing in colour, transparency and internal structure. This suggests the formation of the resins at different stages. Further alteration processes, including fossilization and maturation of the resin in a swamp environment resulted in stepwise aromatization of the cyclohexane ring in steroids and cross-linking through formation of ester bonds as well as carbon–carbon bonds between steroid molecules. The various environmental and geological conditions affecting the formation processes of the resins were recorded in their physico-chemical properties. Additionally, heating conditions accelerated by volcanism were proposed as a factor determining the maturation grade of the resin.

Comparative studies of fossil resins of various ages, botanical sources, geological environments, and provenience were provided via a handheld portable Near-Infrared (NIR)-Raman spectrometer and benchtop instrument both working with laser line 1064 nm. The recorded Raman spectra of individual fossil resins were found to be sufficiently similar irrespective to the device type applied, i.e., handheld or benchtop. Thus, the portable equipment was found to be a sufficient tool for the preliminary identification of resins based on botanical and geographical origin criteria. The observed height ratio of 1640/1440 cm⁻¹ Raman bands did not correlate well with the ages of fossil resins. Hence, it may be assumed that geological conditions such as volcanic activity and/or hydrothermal heating are plausible factors accelerating the maturation of resins and cross-linking processes.

Agate samples collected from the vicinity of Asni and Agouim (Western Atlas, Morocco) were investigated using microscopic observations supported by Raman micro-spectroscopy. The agates are marked by the presence of various microtextures typical of epithermal vein deposits, including jigsaw-puzzle, feathery, and lattice-bladed. The first two indicate that the formation of agates was likely marked by recrystallization of metastable silica phases (i.e., opaline silica or massive chalcedony). The presence of lattice-bladed (after barite and calcite) quartz may be, in turn, ascribed to the boiling-related conditions that could have triggered the formation of abundant copper and iron sulfides found within silica matrix. Additionally, the local occurrence of growth lines (so-called Bambauer quartz) and intergrowth of length-slow and length-fast chalcedony are linked to the variations of physico-chemical conditions during rock formation (alkaline-acidic). According to Raman spectroscopy, silica matrix of the agates is made of α-quartz with a local admixture of moganite (from 0.0 up to 78 wt.%), but also contains numerous solid inclusions of hematite, celadonite, as well as poorly-organized carbonaceous material and rutile. These phases were likely emplaced during low-temperature hydrothermal activity of SiO₂-bearing fluids that originated from post-magmatic hydrothermal activity developed within host rocks and/or meteoric waters.

Outcrops of natural blue and purple halite crystals have been found in Kłodawa (Poland) salt deposit originating from the Permian (Zechstein) salt formation within tectonic zones. Field works carried out on various levels of Kłodawa Salt Mine indicated differences both in intensity of the hue and in the size of the outcrops. Their occurrence was connected with the presence of epigenetic sediments rich in potassium. For the samples of blue halite, an optical anisotropy (birefringence) was observed for both standard mineralogical thin sections and thick plates, indicating a deviation from cubic symmetry. The blue colouration of the halites, described by ultraviolet–visible spectroscopy, is due to the presence of colour centres. The colour centres have been recently identified as: F, R₁ (F₃), R₂ (F₃), M and plasmons (Wesełucha-Birczyńska et al., Vib Spectrosc 60:124–128, 2012). The trace amount of impurities detected in the blue halites by means of scanning electron microscopy–energy dispersive X-ray spectroscopy and micro-X-ray fluorescence techniques were connected mainly with solid inclusions such as K _x Na_{(1 − x)}Cl, KMgCl₃·6H₂O, KCl, orthorhombic sulphur, quartz and some other phases like pyrite. Crystallographic data obtained by X-ray diffraction experiments for the single crystals of the halite from Kłodawa with different saturation of blue or purple colours, as well as for natural colourless halite, revealed lowering of space-group symmetry to monoclinic, orthorhombic, trigonal, tetragonal or even triclinic systems while the space group typical for pure NaCl is Fm-3m.

The amber-bearing coaly shale from the La Cumbre deposit (Cordillera Septentrional, Dominican Republic) contains a large quantity of altered, coalified plant detritus. The coals in these shales are in the transition stage from meta-lignite to subbituminous coals. They are composed mainly of inertinite macerals such as fusinite, semifusinite, macrinite and secretinite. Fossil resin found in the deposit occurs in two forms: detrital grains up to several centimetres in size (type I) and very fine authigenic grains, of a few micrometers in size, inside the humic laminae (type II, resinite). The detrital fossil resins are transparent, with few mineral and organic inclusions. In their composition they contain sulfides, which may come from sulfate reduction, inclusions of plants and/or insects or be caused by volcanic activity developed in surrounding coal series. The resinites are strongly saturated with various inclusions and spatially associated with framboidal pyrite aggregates. Both fossil resin types were probably deposited in a shallow coastal lake environment in the zone bordering the floodplain of the river, with periodic floods. The marine environment conditions, which were progressively changing from oxidizing to reducing, are likely associated with the formation of the fossil resin.