The Earth Story

nscrystals

Tanzanite - Merlani Hills, Tanzania. Available.

Tanzanite! Famously colorful Zoisite from Tanzania. This particular crystal tickled me when I was taking a video of it with a friend and she pointed out how striking of a phantom it seemed to have and when I looked I was struck to see such a remarkable phantom in a Tanzanite. I had seen others but never so prominently. I was further delighted when I looked into the c-axis and saw a nice red color on the edges, a fair indication that the crystal was not treated apparently. Unfortunately I have not read the article yet that this was published in to determine the reasoning behind the assertion yet.

canadiangemassoc

Pleochroism is the optical phenomenon of a gemstone appearing different colours at different angles. Tanzanite is a spectacular example of a trichroic stone, showing 3 distinct colours at different angles.

alandhart

Great excitement a few years ago (Nov 2002) when a new ‘caesium rich beryl’ was discovered in a granitic pegmatite at Ambatovita, Madagascar. The Sakalavana pegmatite main find was a large zone ~6 metres below surface, containing numerous vugs with an estimated 40Kg of material recovered (with smoky quartz, spodumene, tourmaline), mainly fragments and masses of a few grams of low quality and often very corroded. Analysis showed that the mineral was actually a new species of the Beryl group with high caesium (11-15%) and lithium content, and was named Pezzottaite. Rarest of all the specimens are good quality crystals with much of the find being corroded or suitable only for carving or cabochons. This piece is just crazy huge and at 814 carats the largest I have seen! An almost solid ‘plate’ of Pezzottaite crystals over 10cm long, showing typical ‘hexagonal’ form although the species is actually trigonal. The crystals are distinctive with large flat pinacoid faces with smaller modifications and although hard to see on small specimens, with this it is easy to pezzottaite’s great pleochroism. As you look straight down the ‘c-axis’ a bright peachy-raspberry red is revealed, however as I slightly turn the specimen it changes to a more violet hue as we approach the side (the prism direction). The colour has been shown to be caused by radiation induced colour centres involving Mn3+, the radiation most probably derived from 40K in the K-Feldspars in the pegmatite and could account for the smoky quartz and morganite found as associated minerals. I am slightly(!) envious of my friend Dr Federico Pezzotta whom after the species is named 😎. Unlike most new species discovered, it is truly rare to find one that occurs in such large crystals and even more so one that can be used as a gem material! There has been a number of smaller discoveries elsewhere, but none come close to this deposit which is apparently worked-out. This great specimen is just phenomenal and am glad I was able to share it! Thanks

@granada.gallery

• Check out this amazing natural Tanzanite crystal displaying its beautiful pleochroism against a polarized blank computer screen !! •

~ Tanzanite (233.14ct) •

~ Merelani, Arusha, Tanzania •

~ Available / DM or Email: [email protected] for Inquiries

alandhart

10k followers! Just *THANK YOU* to all who do and contribute and enjoy this world of wonder 🙏🏼 | So a short video, but a killer! Spodumene! Described in 1903 by George F. Kunz (American Mineralogist and vice president of Tiffany and Co., New York) the new lilac variety of spodumene also named in his honor. An ore of lithium but also a beautiful gem material. In the Ocean View mine (Pala, San Diego Co., California) in December 2010 in an area called the Big Kahuna II zone, a major find of deep purple kunzite was found. This one called the “Big Kahuna” is the largest and most likely largest gem quality crystal of the species from the USA, 28 x 15.6  x 2 cm and 2.2kg (!) A beautiful and typically striated  flattened crystal, of great colour that due to its pleochroism deepens to a beautiful deep lilac down its top (you should see it lit up the c-axis 😳). Also, that amazing ‘herringbone’ pattern and the slight re-entrant angle? Looks like a twin to me! When the box opened and I first saw this I was speechless. I have seen the great crystal at Harvard and the American Museum, but this one is BIG! I was lucky enough to have a private trip down the mine and see the ‘pocket zone’ hole it came out of, what an amazing experience, wish I had found it! But these things don’t come along often 😎. | Private Collection |

desertqueenminerals

One more example of eye-visible pleochroism! This beautiful cat’s eye tourmaline shows us it’s dichroic, 2 awesome colors bluish-green face up and a pure green from profile. This is done without a polarizing filter! It’s common for tourmaline to be darker down the c-axis, lookin the length of the crystal from top or bottom, and its dichroism can be two tones of the body color instead of two separate hues. This cab also shows us some very nice growth tubes running the c-axis, which creates the cat’s eye.

pmcrystalscollection Tabular chrome dravite tourmaline from Tanzania, showing pleochroism, in front of a polarized screen.

physicsfun Magic Sun Stone: gem quality iolite shows very strong pleochroism- its color depends on the polarization of light as it is transmitted through the crystal. The color of this rough iolite gemstone changes dramatically from clear to opaque purple as the orientation of a linear polarizing filter is rotated through 90 degrees. Also known as a "Viking sky compass" since it can detect the polarization of sunlight in the sky and thereby locate the sun for navigation even on cloudy days or when the sun is below the horizon- useful for this time of year far north. ➡️ Follow the link in my @physicsfun profile for more information and where to buy a "magic sun stone" and some polarizing filters. #pleochroism #dichroism #cordierite