An emerald is a mineral gemstone and a variety of beryl. It is the birthstone of someone whose birthday is in the month of May. It is a green crystal. The emerald is one of the most valuable gems, along with the ruby, the opal, topaz, the diamond, and a sapphire.
|Crystal symmetry||(6/m 2/m 2/m) – Dihexagonal Dipyramidal|
|Unit cell||a = 9.21 Å, c = 9.19 Å; Z = 2|
|Crystal habit||Massive to well Crystalline|
|Crystal system||Hexagonal (6/m 2/m 2/m) Space group: P6/mсc|
|Cleavage||Imperfect on the |
|Mohs scale hardness||7.5–8|
|Diaphaneity||Transparent to opaque|
|Specific gravity||Average 2.76|
|Optical properties||Uniaxial (-)|
|Refractive index||nω = 1.564–1.595,|
nε = 1.568–1.602
|Birefringence||δ = 0.0040–0.0070|
|Ultraviolet fluorescence||None (some fracture filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)|
The word emerald comes from Vulgar Latin. The word was Esmaralda/Esmaraldus, a different way of saying the Latin word Smaragdus, which came from the Greek, σμάραγδος (smaragdos; "green gem"). It first came from a Semitic word, izmargad (אזמרגד). This meant "emerald" or "green". The name could also be related to the Semitic word baraq (בָּרָק ;البُراق; "lightning" or "shine") (c.f. Hebrew: ברקת bareqeth and Arabic: برق, barq, "lightning"). It is where the Persian (زمرّد zomorrod), Turkish (zümrüt), Sanskrit (मरग्दम् maragdam) and Russian (изумруд; izumrúd) words came from.