Alabaster is characterized by the crystal size (less than 0.05 mm) disposed in an intimate framework that confers alabaster translucency and compactness. The first of these qualities provides alabaster with its characteristic beauty; the second one, combined with gypsum’s low hardness, is what makes this material so valuable. On the other hand, alabaster is easily stained with iron oxides.
Yet, alabaster also has disadvantages. As previously stated, due its propensity to lose water molecules, the mineralogical composition of a sample can be partially or completely modified when applying heat (alabaster starts to decompose at 50ºC) or if samples are exposed to special humidity conditions. It should also be taken into account that alabaster is a water soluble salt, which results in a limitation of use depending on the environmental conditions to which it is going be exposed.
• Boulder: It is the raw stone, as extracted from the quarry, or cleaned from clays or loose fractions, with no other treatment.
• Veins: Bands of colour that is different from the colour at the base. They may be more or less continuous along the block. Generally veins are the result of the existence of clay impurities and they do not involve mechanic discontinuities in the stone.
• “Aguas”: More or less translucent patterns may appear within the base colour, which are due to the size and packing of the microscopic crystals, can be occur. They do not involve mechanical discontinuities in the stone.
• “Frías (or fleas)”: Mechanical discontinuities in the rock. They are clay veins that cross the rock dividing it into separate blocks.
• Salts: Bands or nodules integrated by gypsum crystals.
• “Coquera”: Holes that appear inside the stone. They are normally smaller than 4-5 cm and their walls may be draped with gypsum crystals.
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