The Sardius Carnelian gemstone is assigned to the Angelic Order of the Seraphim.
"The Seraphim are the highest order or choir of angels. The God-loving six-winged Seraphim stand closer than all before their Creator and maker, as the prophet Isaiah saw, saying: "And the seraphim stood around Him, each having six wings" (Isaiah 6:2).
Standing before such glory, the seraphim are fire-like, as it said: "Who maketh his angels spirits; his ministers a flaming fire" (Ps 103:4). "For our God is a consuming fire." (Heb 12:29); "His throne was a flame of fire" (Dan 7:9); "the appearance of the Lord was like a blazing fire" (Ex 24:17).
The Seraphim are aflame with love for God and kindle others to such love, as is shown by
their very name, for "seraphim" in the Hebrew language means: "flaming"."
-St. Dimitry of Rostov, 17th Century Saint, Hierarch & Ascetic
[Serfes. Fr Demetrius. Orthodox Teachings on the Holy Angels. (reprint) Minea of St. Dimitry of Rostov.
Orthodox Life. December 1968.]