Marble is a metamorphic rock predominantly consisting of calcite, dolomite and crystals. Onyx originates from deposits of limestone caverns, where it forms stalactites and stalagmites. Onyx is formed by gentle, dripping water movement and may envelop terrestrial fossil remains. Since onyxes are formed by a process of crystallization, they are considered part of the marble family. Marbles and Onyxes typically have a diverse aesthetic appeal, accentuated by distinct veining and often bold colors. They are relatively softer than granite. Marbles can be scratched by kitchen utensils, so it is best to use cutting boards and other protective measures. Marbles can also be etched by chemical attack. Since these stones are calcium carbonate-based, they can be damaged by exposure to acidic solutions such as lemon juice, tomatoes, vinegar, etc. The use of inappropriate cleaning agents may also trigger acidic attack. Acidic solutions can permanently etch the surface of the material. The application of a sealer will reduce, but not eliminate, the vulnerability to acidic attack. For these reasons, marbles and onyxes are not recommended for use in kitchens, however they can be a good selection for bathroom vanities for example.