Cinnabar: Red as dragon blood and optically active

Cinnabar

• probably named after the Persian word for dragon blood because of its characteristic red colour
• used since ancient times as a pigment
• Formula: HgS
• Space group: P3₁21 (No. 152) or P3₂21 (No. 154)
• Crystal system: trigonal
• Crystal class: 32
• Lattice parameters: a = b = 4.1347(6) Å, c = 9.4451(3) Å, α = β = 90°, γ = 120°

---

Modified by CombineZP

Picture: JJ Harrison (jjharrison89@facebook.com) – CC BY-SA 3.0

---

Crystal structure (click on the pictures to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).)

View along the c axis.

View along the a axis.

• the crystals structure is characteristic of chains with alternating sulfur and mercury atoms, which form helices with the helix axis running parallel to the c axis.
• These helices are also the reason why crystals of cinnarbar are optically active (see: A.M. Glazer, K. Stadnicka, “On the origin of optical activity in crystal structures”. J. Appl. Cryst. 19 (2), 1986, 108–122. doi:10.1107/S0021889886089823

Advertisement