The GEMHUNTER

Professor Hausel's Guide to Finding Gemstones, Diamonds, Gold, Rocks & Minerals 

Beryl - A Mineral of many Gems


VARIETY

COLOR

CHROMOPHORES

Emerald

Chrome-green

Cr, V, Fe2+, Fe3+

Aquamarine

Light blue to sea green

Fe2+, Fe3+

Maxixe beryl`

Blue (fades in sunlight)

Fe2+, Fe3+

Chrysolite

Yellow-green

Fe2+, Fe3+

Golden beryl

Golden-yellow

Fe2+, Fe3+

Heliodor

Greenish-yellow

Fe2+, Fe3+

Morganite

Pink-orange, pale pink

Mn2+, Mn3+

Bixbite (Red Emerald)

Dark-red

Mn2+, Mn3+

Goshenite (Rosterite)

Colorless

None

Varieties of gem beryl and trace coloring agents (chromophores) responsible for color in the gemstones.

Beryl is a mineral of many gems and when gem-quality, it can occur as emerald, aquamarine or precious berylBeryl (Be3Al2Si6O18) forms distinct 6-sided hexagonal crystal prisms that are capped by flat, basal, pinachodial terminations such as seen in the photo to the left (specimen collected at Casper Mountain, Wyoming). The crystal habit is often distinct; thus, recognizing the crystal habit along with beryl found in granite pegmatite (very coarse-grained granite) is often all a geologist or prospector needs to verify the presence of beryl. Helidor and aquamarine are usually the more common varieties. 


Gem varieties of beryl are all the same mineral: they just have trace coloring agents known as chromophores that give them different colors. So, yes, that extremely expensive emerald is the same mineral as that not so attractive helidor - the only difference (beside price) is just a little bit of chrome in the crystal structure of the emerald.


Much of the beryl found in pegmatite is greenish-yellow, translucent to opaque with moderate specific gravity (2.6 to 2.9) similar to quartz (2.7). Thus, when panning for gold, any beryl accidentally captured in a gold pan could easily be rejected (washed out) with quartz and other light materials. Thus, beryl has moderate heft - a hand-sized specimen will not feel abnormally heavy when bounced in your hand. With a hardness of 7.5 to 8 on Moh's scale similar to quartz (H=7) and topaz (H=8), it is plenty hard enough to produce long lasting gemstones. Because of its favorable hardness, beryl will yield a white streak when scratched by a knife or scraped across a streak plate (Hausel, 2009; Hausel and Sutherland, 2000).


Beryl has vitreous luster on 'fresh' surfaces and will produce conchoidal to uneven fracture. It has imperfect basal c{0001} cleavage. When found as transparent crystals, beryl is gem quality. Depending on color, beryl will yield a variety of gems. These are typically separated into three groups - aquamarine (light blue), emerald (chrome-green) and precious beryl (all other colors).


Most beryl will tend to crystallize out of felsic magma; particularly beryllium (Be) enriched rhyolite and pegmatite. The great emerald, aquamarine and precious beryl deposits of Brazil (and elsewhere) are associated with pegmatite and eluvial deposits, while some other beryl may have hydrothermal (hot fluid) or metamorphic (recrystallized) genesis. Secondary deposits are important in specific regions of the world (i.e., Brazil and Sri Lanka) where beryl has been naturally beneficiated in eluvial and colluvial deposits during erosion. So, when you are searching for beryl gemstones, look for pegmatites and check any geology literature about any igneous rocks and pegmatites in the region. If there is a mention of anomalous beryllium associated with granite, rhyolite or granite pegmatite, you are in the right area. In my recent 368-page book, A Guide to Finding Gemstones, Gold, Minerals and Rocks, I examined some very interesting areas with known Be-enriched pegmatites and described where many are located that have never been explored - any of which could yield common beryl or gemstone-beryl. So if you want to be a serious gem prospector - you should have a copy of my book. And don't forget to share: buy many additional copies for all of your friends, relatives and neighbors.


Stream placers are unfavorable for beryl because of the mineral's low specific gravity and prominent basal and rhombohedral parting. Disaggregation by abrasion will often result in disintegration of the mineral over short stream transportation distances. Thus, the more important gem-beryl deposits are secondary eluvial or colluvial deposits. If you find gem-quality beryl in your gold pan while panning, it indicates that the source of the gem is in the immediate area. 


Beryl may be bluish-green, light-yellow, emerald-green, golden-yellow, yellow-green, pink, reddish-pink, raspberry-red or colorless. Some of the more popular colored beryl gems are aquamarine, emerald, bixbite (red emerald), golden beryl, goshenite, heliodor and morganite. Rarely, beryl gemstones are colored by mineral inclusions (i.e., microscopic spinel) such as black beryl from Mozambique and Madagascar.


Of the beryl gems, emerald is often the most fragile due to uneven substitution of Cr (chromium) within the crystal lattice that produces internal flaws. Thus, most emeralds have minute fractures and zones of translucency intermixed with zones of transparency. Brightly colored beryl is often faceted in step or combined forms, whereas pale beryl is cut into brilliants to enhance luster. Some rare beryl has been found with asterism or silky luster caused by inclusions of epidote and apatite. These are cut into cabochons to display asterism or cat’s eyes (Kievlenko, 2003).


Some beryl specimens have included very large stones. These include the enormous 6-foot long crystal of 2.5 tonnes (Bauer 1968b)! Another giant specimen was found in Albany, Maine that was described to be 27 feet long and weigh >25 tonnes (Hurlbut and Switzer 1979)!


Aquamarine and many precious beryl crystals are found in granite pegmatites. Much high-quality emerald is recovered from hydrothermal deposits that are not favorable for large gems, and most emeralds are considerably smaller than other beryl gems. Some extraordinary emeralds have been mined in Columbia, including a 1,759-carat doubly terminated emerald (Ward 2001a). Another large emerald, known as the Gachala, weighed 858-carats and measured 2 inches in length – this stone resides in the Smithsonian collection and is regarded as one of the finest emeralds.


Aquamarine is periodically found as very large crystals. One of the larger, the Papamel, was found in Minas Gerais Brazil in 1910. The specimen weighed 553,400 carats (244 lbs) at 18 inches long and 15.5 inches wide. It was so transparent that one could read through the stone from end to end. The stone was cut into many gems of total weight >100,000 carats (Sinkankas 1991)! Another large stone from Brazil was the Domo Pedro of 10,363 carats that yielded the largest cut aquamarine gemstone. Another large aquamarine was found at Anderson Ridge in the Wind River Mountains of western Wyoming by friend of mine and also a prospector by the name of Elmer Winters. The specimen weighed many thousands of carats, had excellent transparency and from what I remember, it was about 1-foot long (Hausel, 1991).


Because of large size and perfect hexagonal habit of beryl in some pegmatites, some extraordinary industrial specimens have been recovered that have no value as gems. Many of these, because of crystal perfection and size are mentioned as collector and museum specimens. For example, extraordinary specimens found at the Triple Chance mine in the Broken Hill district of Australia, were flawed, green, brown and blue-green beryl prisms up to 4 feet long and 18 inches wide. At the Lady Beryl mine, 2.5 miles south of the Triple Chance, 12 tonnes of crystals were produced, some of which were described as projecting from the pegmatite like fence posts. The largest was (3 x 9.5 feet).