Abstract:The
Cave of Giant Crystals of Naica (Chihuahua, Mexico) is a world
geological treasure worth to be preserved. These crystals of up to
12 m in length are made of selenite, the macrocrystalline variety
of gypsum (CaSO4·2H2O). They have grown
for thousands of years until the cave was dried, which allowed the
cave and the crystals to be accessible, but exposed their surfaces
in contact with air. Gypsum crystals are fragile because of their
trend to dehydrate, the possible replacement to CaCO3 upon
reactions with a… Show more
“…At the left is displayed the Fe, As–Pb, and Cu correlation map, and the Pb signal intensity of the same region. At the right is shown Pb L 3 -edge XANES spectra collected in fluorescence yield mode on different samples and areas containing Pb (Castillo-Sandoval et al ., 2015). Figure 7. μ -XRF mapping of a surface region of sample GYP001 of the CC and μ -XANES spectra of Pb L 3 -edge from 14 different ROI taken on the four samples GYP001 to 004.…”
The giant gypsum crystals of Naica cave have fascinated scientists since their discovery in 2000. Human activity has changed the microclimate inside the cave, making scientists wonder about the potential environmental impact on the crystals. Over the last 9 years, we have studied approximately 70 samples. This paper reports on the detailed chemical–structural characterization of the impurities present at the surface of these crystals and the experimental simulations of their potential deterioration patterns. Selected samples were studied by petrography, optical and electronic microscopy, and laboratory X-ray diffraction. 2D grazing incidence X-ray diffraction, X-ray μ-fluorescence, and X-ray μ-absorption near-edge structure were used to identify the impurities and their associated phases. These impurities were deposited during the latest stage of the gypsum crystal formation and have afterward evolved with the natural high humidity. The simulations of the behavior of the crystals in microclimatic chambers produced crystal dissolution by 1–4% weight fraction under high CO2 concentration and permanent fog, and gypsum phase dehydration under air and CO2 gaseous environment. Our work suggests that most surface impurities are of natural origin; the most significant anthropogenic damage on the crystals is the extraction of water from the caves.
“…At the left is displayed the Fe, As–Pb, and Cu correlation map, and the Pb signal intensity of the same region. At the right is shown Pb L 3 -edge XANES spectra collected in fluorescence yield mode on different samples and areas containing Pb (Castillo-Sandoval et al ., 2015). Figure 7. μ -XRF mapping of a surface region of sample GYP001 of the CC and μ -XANES spectra of Pb L 3 -edge from 14 different ROI taken on the four samples GYP001 to 004.…”
The giant gypsum crystals of Naica cave have fascinated scientists since their discovery in 2000. Human activity has changed the microclimate inside the cave, making scientists wonder about the potential environmental impact on the crystals. Over the last 9 years, we have studied approximately 70 samples. This paper reports on the detailed chemical–structural characterization of the impurities present at the surface of these crystals and the experimental simulations of their potential deterioration patterns. Selected samples were studied by petrography, optical and electronic microscopy, and laboratory X-ray diffraction. 2D grazing incidence X-ray diffraction, X-ray μ-fluorescence, and X-ray μ-absorption near-edge structure were used to identify the impurities and their associated phases. These impurities were deposited during the latest stage of the gypsum crystal formation and have afterward evolved with the natural high humidity. The simulations of the behavior of the crystals in microclimatic chambers produced crystal dissolution by 1–4% weight fraction under high CO2 concentration and permanent fog, and gypsum phase dehydration under air and CO2 gaseous environment. Our work suggests that most surface impurities are of natural origin; the most significant anthropogenic damage on the crystals is the extraction of water from the caves.
“…At rates as high as 1 mm per week, Ricci et al [23] observed a rapid rate of dissolution of both in vitro and in vivo gypsum from the outer surface inwards. Despite this dissolution, they reported [14]. that while bone was not observed to come into direct contact with gypsum, gypsum stimulated new bone formation.…”
Section: Gypsum Bone Cementsmentioning
confidence: 99%
“…As a result, the α-form results in a super thick, heavier and less soluble dihydrate than the β-form [11]. The formed gypsum exhibits a layered structure with the water molecules alternating with calcium sulfate layers explaining this mineral's easy cleavage [14], as shown in Figure 4. The hemihydrate has the water molecules arranged in channels between chains of calcium sulfate.…”
Hard tissues are natural nanocomposites comprising collagen nanofibers that are interlocked with hydroxyapatite (HAp) nanocrystallites. This mechanical interlocking at the nanoscale provides the unique properties of hard tissues (bone and teeth). Upon fracture, cements are usually used for treatment of simple fractures or as an adhesive for the treatment of complicated fractures that require the use of metallic implants. Most of the commercially available bone cements are polymer-based, and lack the required bioactivity for a successful cementation. Besides calcium phosphate cements, gypsum is one of the early recognized and used biomaterials as a basi for a self-setting cementation. It is based on the controlled hydration of plaster of Paris at room temperature and its subsequent conversion to a self-setting solid gypsum product. In our work, we have taken this process further towards the development of a set of nanocomposites that have enhanced bioactivity and mechanical properties. This chapter will outline the formation, characterization, and properties of gypsum-based nanocomposites for bone cement applications. These modified cements can be formulated at room temperature and have been shown to possess a high degree of bioactivity, and are considered potential candidates for bone fracture and defect treatment.
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