Alabaster is a beautiful, soft mineral or rock valued for centuries in art and decoration. Its delicate appearance and workability have made it a favored medium for crafting intricate objects and architectural elements across various cultures. This article explores its geological origins, distinct physical traits, historical applications, and practical identification methods.
What Alabaster Is
Alabaster refers to two distinct mineral forms. The most common type is gypsum alabaster, a hydrous sulfate of calcium with the chemical formula CaSO₄·2H₂O. This variety typically forms through the sedimentary deposition of minerals in environments where water containing dissolved calcium sulfate evaporates, such as shallow basins or lagoons.
The other type is calcite alabaster, also known as onyx-marble or Egyptian alabaster. This form consists of calcium carbonate (CaCO₃) and is geologically classified as a compact, banded travertine stone or stalagmitic limestone. Calcite alabaster forms from the precipitation of calcium carbonate, often in cave environments or hot springs.
Unique Physical Properties
Alabaster is recognized for its distinctive physical attributes. Its typical colors range from pure white to off-white, cream, and beige, often exhibiting brown clouding or veining due to iron oxide impurities.
A notable property of alabaster is its translucence. This characteristic gives alabaster a soft, diffused glow when illuminated, making it particularly suitable for lighting applications. The stone also possesses a fine and uniform texture, often described as smooth to the touch. Alabaster is a relatively soft material, with gypsum alabaster having a Mohs hardness of 1.5 to 2, and calcite alabaster a Mohs hardness of 3. This softness makes it easy to carve into intricate forms but also renders it susceptible to scratches and damage.
Uses Throughout History
Alabaster has been utilized across diverse cultures and eras. Ancient civilizations, including the Egyptians and Mesopotamians, extensively employed gypsum alabaster for small sculptures and vessels. Egyptian artisans crafted canopic jars, sacred objects, and sarcophagi, such as that of Seti I, from calcite alabaster. In Mesopotamia, it was the material of choice for figures of deities and devotees in temples, including the substantial Assyrian palace reliefs.
During medieval Europe, gypsum alabaster was widely used for religious sculptures and altarpieces in churches and monasteries. Its soft nature allowed for detailed carving. The translucency of alabaster also led to its use in windows, where thin sheets could diffuse natural light.
In contemporary times, alabaster remains a popular material for artistic and decorative purposes. Modern sculptors use it for intricate carvings, while designers incorporate it into architectural accents. Its light-diffusing properties make it suitable for lighting fixtures, such as lamps and translucent panels. Alabaster also finds its way into decorative household items like vases and bowls, and even into jewelry and fashion.
How to Identify Alabaster
Distinguishing alabaster from other similar materials relies on a few observations. Its most defining characteristic is its relative softness. Gypsum alabaster is soft enough to be scratched by a fingernail (Mohs hardness 1.5 to 2). Calcite alabaster, while slightly harder (Mohs hardness 3), can still be scratched with a knife.
Another key indicator is its translucence, creating a soft glow. This contrasts with materials like marble, which is generally harder (Mohs hardness 3-5) and more opaque. True onyx, often confused with banded calcite alabaster, is significantly harder (6.5 to 7 on the Mohs scale) and exhibits more defined banding rather than the subtle, cloudy veining often seen in alabaster. Characteristic veining, appearing as swirling bands or clouding, also aids in identification.