Spinel occurs in a variety of colours, from white and black, to shades of grey, blue, purple, orange, green, teal and red. Bright red and blue spinel are the most valuable of its colour spectrum. The pure blue coloration of spinel is caused by small quantities of cobalt. Cobalt bearing spinel is rare and highly prized.
Red spinel has been mistaken for ruby over the centuries and some of the most famous “rubies” in the crown jewels are in fact, red spinels, including the famous Black Prince's Ruby in the Crown of England.
Ruby has received wonderful marketing over the past two centuries which is reflected in its price tag. Spinel was for a time left on the shelf, relegated as a collector’s stone. Luckily things are changing and this princely gem is receiving the recognition it deserves. So many rubies are heat treated and fracture filled while the price of pink diamonds is unobtainable for most people. Spinels remain mostly untreated and have an amazing, almost diamond-like sparkle and transparency while most rubies have a cloudiness due to silk and inclusions. There are many world sources and prices are still competitive, however are now rising quickly.
Fine red and blue spinel is more rare than corundum (ruby and sapphire) of equal colour but costs on average 30% less.
Spinel has excellent hardness (7.5-8 on the Mohs hardness scale) and durability, making it the perfect gem for rings worn daily, such as engagement rings. Like any other precious gem, it should be treated with care, and spinel rings should be removed prior to exposure to harsh chemicals or abrasive surfaces, and tasks such as gardening or gym, where it could get damaged.
Cobalt bearing blue spinel and pure red spinel are the most valuable colours, with bigger gems of vivid colour and high clarity commanding considerable prices. Red spinel is the most expensive red gem next to ruby and the rare red diamond. Bigger gems of high clarity and lustre in blue-grey, grey and pink are also rare and continuing to increase in value.
Sri Lanka, Thailand, Myanmar (Burma), Vietnam, Tajikistan, Afghanistan, Tanzania, Kenya and Madagascar.
Unlike sapphire and ruby, spinel is generally not treated.
Spinel has been synthesised for industrial purposes since around 2000. Synthetic spinel looks like glass but has notably higher strength against pressure. The first synthesis of spinel occurred in the 19th century, and in the 1930s synthetic spinel was a popular substitute for a number of natural gems such as aquamarine, emerald, tourmaline and ruby.
Hardness: 7.5-8 Mohs
Specific Gravity: (Depending on the composition) The rare Zn-rich spinel can be as high as 4.40, otherwise it averages from 3.58 to 3.61.
Refractive Index: 1.719
Crystal Form: Octehedra or flat triangular plates caused by twinning
Special Care: None
Durability: Very good