OVERVIEW
ABOUT TOURMALINE
Tourmaline’s colors have many different causes. It’s generally agreed that traces of iron, and possibly titanium, induce green and blue colors. Manganese produces reds and pinks, and possibly yellows. Some pink and yellow tourmalines might owe their hues to color centers caused by radiation, which can be natural or laboratory-induced.
BIRTHSTONES & ANNIVERSARIES
Tourmaline is a birthstone for October, along with opal. Tourmaline is also the gem of the eighth anniversary.
1554
Francisco Spinoza’s expedition discovers “Brazilian emerald”: the first recorded green tourmaline crystal.
PYROELECTRIC
Tourmaline becomes electrically charged when heated. Also when squeezed: it’s piezoelectric too.
PARAIBA
Brazilian source famous for vivid blue to green tourmalines colored by copper.
FACTS
Mineral: Tourmaline
Chemistry:
Elbaite Na(Li1.5,Al1.5)Al6Si6O18(BO3)3(OH)4
Dravite NaMg3Al6Si6O18(BO3)3(OH)4
Liddicoatite Ca(Li2Al)Al6Si6O18(BO3)3(OH)3F
Chromedravite NaMg3Cr6Si6O18(BO3)3(OH)4
Color: All colors
Refractive index: 1.624 to 1.644
Birefringence: 0.018 to 0.040
Specific gravity: 3.06 (+0.20, -0.06)
Mohs Hardness: 7 to 7.5
TREATMENTS
There are a number of processes used to alter the color, apparent clarity, or improve the durability of gems.
SYNTHETICS
Some gemstones have synthetic counterparts that have essentially the same chemical, physical, and optical properties, but are grown by man in a laboratory.
Imitations
Any gem can be imitated—sometimes by manmade materials or by natural materials chosen by man to impersonate a particular gem.
1
TRIGONAL SYSTEM
Tourmaline crystallizes in the trigonal system; no other common mineral has three-sided prisms.
2
WATERMELON VARIETY
Watermelon tourmaline is green on the outside and a delicious pink on the inside.
3
LIDDICOATITE
Liddicoatite tourmaline was named for beloved former GIA President Richard T. Liddicoat.
QUALITY FACTORS
Tourmaline’s varieties have a wide range of quality factors considerations.
TOURMALINE QUALITY FACTORS: THE COMPREHENSIVE GUIDE
RESEARCH
Explore sources, gemological research, and the role of gems in history.