Sapphire is a variety of corundum, an aluminum oxide with a hardness of 9. Its crystal system is hexagonal (trigonal). It forms in prismatic, bipyramidal, rhombohedral or tabular crystals, and it can also occur in granular or massive habits. It is found in metamorphic and igneous rocks, as well as alluvial deposits. Although people most often think of Sapphire as dark blue, it is found in a diversity of colors, including many shades of blue, violet, pink, white, green, black, yellow and orange. In fact, all colors of corundum (except red, which is Ruby) are called Sapphire. The coloring pigment of blue Sapphire is iron and titanium, and in violet Sapphire the pigment is vanadium. A low iron content brings about yellow or green Sapphires, and chrome produces pink ones. Sapphire was used by the Etruscans over 2,500 years ago and was also prized in ancient Rome, Greece and Egypt. Revered as a stone of royalty, Sapphire was believed to keep kings safe from harm or envy. It was also purported to protect one from dishonesty, fraud, terror, poverty, and even stupidity and ill temper. The three crossed lines in Star Sapphire have been said to represent hope, faith and destiny, and in German lore it was considered a stone of victory. Although all corundums share some energies in common, the various colors of Sapphire have individual vibrational signatures and different spiritual properties. We will therefore consider them separately.
Simmons, Robert; Ahsian, Naisha. The Book of Stones, Revised Edition: Who They Are and What They Teach (several pages). North Atlantic Books. Kindle Edition.