The butterfly brooch collection is on temporary display in the Gem and Mineral Hall through May 2013. The collection was created and is owned by Buzz and Bernardine, who have a passion for rare gemstones that they have chosen to share through unique jewelry pieces. The butterfly brooches only represent a third of their entire jewelry collection. Buzz faceted most of the main gems and Bernardine designed all except for the "Ninja" butterfly, which is Buzz's creation. All the metalwork is done in 18kt gold.
This brooch is almost entirely set with benitoite, the California state gemstone. A barium-titanium silicate mineral (BaTiSi3O9), benitoite is a rare mineral, crystals large enough to be cut into gemstones are found only in one location: the Dallas gem mine in San Benito County, California. An unusual geologic setting of hydrothermal veins between glaucophane schist and serpentinite created this rare mineral. Benitoite is known for its high dispersion and its vivid blue fluorescence in UV light. While the blue and colorless benitoites are natural, the orange benitoites in the eyes are produced by heat treatment of colorless stones.
A 10.01-ct green hiddenite is the central piece of the brooch. Hiddenite is a green variety of the mineral spodumene (LiAl(SiO3)2) in which the color is caused by small amounts of the element. chromium. Hiddenite from North Carolina is found associated with emerald, the green variety of bery, which also owes its color to chromium. The body of this butterfly is the world's largest faceted hiddenite. It comes from a deposit in North Carolina that is the only important source of hiddenite. The butterfly also contains rainbow feldspar (displaying adularescence) from Madagascar, colorless diamond, and green tourmaline. The eyes are red beryl, the rarest of all varietes of the mineral beryl. Red beryl of gem-quality is found only in the Wah Wah mountains of Utah.
The featured stone of the "Ninja" butterfly brooch is alexandrite (body and eyes). Alexandrite is a variety of the mineral chrysoberyl (BeAl2O4) that displays a particular feature known as “color change”. The picture of the Ninja butterfly on the left has been taken under incandescent light, and on the right under fluorescent light. Tanzanian purple scapolites and Madagascar blue apatites are set around a 3.58ct Russian alexandrite. While these gems do not change color, they do match the color of the alexandrite uder each type of illumination.
This butterfly brooch displays a variety of precious opals from Virgin Valley, Nevada. This deposit was a forested valley buried by volcanic ash approximately 15 million years ago. The buried wood was gradually replaced by opal. The most valuable opals are black with a strong play-of-colors. Nearly all Virgin Valley opal has very high water content, so that as soon as it is removed from the ground it starts to dehydrate, causing it to crack (or “craze”). The stones in this butterfly are remarkably free of cracking and represent the tiny minority of stable opals from this locality.
These natural pearls from the Gulf of California are known as “Baja pearls.” They have been popular since Spanish conquistadors brought them back to Europe. “La Peregrina,” the famous pearl owned by Queen Mary I of England and more recently by actress Elizabeth Taylor, is a Baja pearl. Madagascar rainbow feldspar, colorless diamond and Colombian emerald are also set in this brooch.
This elegant butterfly brooch is set with green peridot from Pakistan, colorless diamond and orange spessartine garnet from California. Peridot is a nickname for gem-quality forsterite. This mineral is one of the most common in the Earth, but most is located deep underground, in the Earth’s mantle.
This butterfly brooch is made entirely of gems from Mexico, including a 13.51ct rhodocrosite (MnCO3). This mineral is very easily scratched, so it is very rare to find it in jewelry; however, its beautiful vivid pink-red color makes it worth some extra care! Apatite and opal cover the wings. The eyes are green chromium-rich titanite (sphene).
Orange spessartine garnets from the Little Three mine in Ramona, California highlight this brooch, along with colorless diamonds and green tsavorite garnets from Kenya. The name "garnet" refers to a group of silicate minerals with the same internal arrangements of atoms, but different chemical compositions. Spessartine (Mn3Al2(SiO4)3) is a manganese-aluminum-garnet popular in jewelry due to its bright shades of yellow, orange or red. Tsavorite is a green variety of grossular ((Ca3Al2(SiO4)3), a calcium-aluminum garnet, with impurities of vanadium and chromium, which give the green color.
This butterfly features gemstones from California: orange spessartine garnet from San Diego County and blue benitoite from San Benito County.
Pink and red spinels from Vietnam are the highlights of this butterfly brooch. Red spinel (MgAl2O4) has long been used as an affordable alternative to ruby, which it closely resembles. Some famous historical rubies are actually red spinels. Spinel is now very popular in its own right. The eyes of the butterfly are blue jeremejevites (Al6(BO3)5(F,OH)3) from Namibia. Although beautiful in faceted gems, jeremejevite is seldom used in jewelry because of its great rarity.
The butterfly brooch is set with three exceedingly rare kinds of gemstone. The body is a 5.07-carat yellow stibiotantalite from Afghanistan. Stibiotantalite, SbTaO4, gets its name from its chemical composition. It is an oxide of antimony and tantalum, “stibium” being the Latin name for the element antimony. The butterfly wings are set with electric-blue haüyne (sodalite group mineral (Na, Ca)4-8 (Al6Si6(O,S)24)(SO4, Cl)1-2) found in small gas cavities in a volcanic rock in Germany, and the eyes are white cassiterite (SnO2), a tin ore from China.
The multi-colored sparkle of this butterfly emanates from its green titanites (a.k.a. “sphene”) from Madagascar. The "fire" of titanite derives from its very high dispersion and combined high index of refraction. Titanite (CaTiSiO5) is a fairly common accessory mineral in igneous and metamorphic rocks, but is very seldom found in size and quality suitable for gems.
This butterfly brooch brings together spectacular titanites in three different colors: green from Madagascar, brown from Pakistan, and yellow also from Pakistan.
Natural unheated tanzanite of many different colors can be seen in this butterfly brooch. Tanzanite is a nickname for gem quality varieties of the mineral zoisite from northern Tanzania. Most stones are vivid blue to purple. Stones that are not heat-treated can display very strong pleochroism.
This butterfly brooch is set with red and pink topaz from Russia, Pakistan and Brazil, along with rainbow feldspars from Magadascar, colorless diamonds and colorless jeremijevites for the eyes. Although most people think topaz is only a yellow gem, in nature most topaz is colorless to pale blue. Topaz gems in shades of deep pink to red are the most prized.
This butterfly brooch is set with blue sapphires from Yogo Gulch, Montana. Sapphire senso stricto is the blue variety of corundum (Al2O3), while the red variety is referred to as ruby. Corundum can come in a variety of colors, and will be then referred as "colored sapphire", such as "pink sapphire", or "yellow sapphire" for example. The blue color is known to be due to charge transfer between titanium (Ti4+) and iron (Fe2+). Yogo sapphires are among the world’s finest sapphires. They are found in a hard igneous rock and because of that, tend to be small crystals and rather difficult to mine. The sapphires are accented by rainbow feldspars from Madagascar and colorless diamonds.
Strong pearly-to-blue floating sheen seen in the moonstone varieties of the feldspars Orthoclase, Albite, and Oligoclase.This is due to the diffraction of light on closely spaced layers of feldspar of slightly different composition (also called Schiller effect).
A color-change gemstone refers to a gem that changes color when illuminated under different lighting conditions. The typical example is alexandrite (a color-change chrysoberyl). Lights never display a perfect uniform emission of the visible light: some wavelengths can be more transmitted than others. For example, the sun is rich in blue light (also true for fluorescent light), while incandescent light (candle light for example) emits more red. Alexandrite has two "transmission windows" (due to the absorption of the element chromium): one in the blue and the other one in the red. When subjected to fluorescent or sun light, the stone will therefore appear blue, while it will appear purplish-red under incandescent light (combination of red and blue colors). Other gemstones can present this effect, such as sapphire or garnet for example.
The color of light depends upon its wavelength. Normal white light contains a mix of all visible wavelengths and includes red, orange, yellow, green, blue, and violet (from longer to shorter wavelength). When a beam of light enters a transparent solid at an angle, it is refracted (the angle of the beam is changed). Longer wavelengths of light are refracted more than shorter wavelengths, so the material separates white light into its component colors. This phenomenon is called dispersion. Minerals differ in their ability to create dispersion. Diamond produces strong dispersion, which is the reason that one is able to see distinct flashes of color in an otherwise colorless diamond gem. The dispersion defines how efficiently a material splits white light into a rainbow (like a prism, see figure below).
In a more scientifically way, it is a measure of the angular separation of refracted light of different wavelengths (specifically, blue light at 430.8 nm and red light at 686.7 nm) within a given material. Diamond has a fairly strong dispersion value of 0.044, while titanite (sphene) has a very strong dispersion value of 0.051.
The fire of a gemstone refers to the flashes of color emitted by this gemstone. It depends on the dispersion, the cut angles, the lighting environment and the refractive index. For example, under same illumination and with a similar cut, titanite (sphene) will show more fire than diamond, which itself show much more fire than quartz.
When a beam of light strikes the surface of a transparent material at an angle, part will be reflected away and part will penetrate the material. The part of the beam that enters the material will be bent or refracted by an amount related both to the angle at which the beam strikes the material (the angle of incidence), to the density of the material, and to the light absorbing properties of the material. In general, the denser a material, the more the light entering it will be bent, but because additional factors affect the bending, this determination is not the same as a measurement of the density. Also the amount of bending may vary with wavelength of the light. By measuring the angles of incidence and refraction, a quantity called the index of refraction can be determined. This index can be used as an identifying characteristic for the material.
At the contact of substances with different index of refraction, the light will be bent, with an angle defined by the relation: η1 sin(θ1) = η2 sin(θ2), where η1 and η2 are the index of refraction of 2 different materials, and θ1 and θ2 the angles of the propagating light, for material 1 and 2 respectively. By definition, the index of refraction of air is η = 1. The index of refraction of opal is 1.45 and of diamond is 2.435. Observe below the effect of the incident light on the refracted ray in these two different minerals.
The play-of-color effect of opal is due to its internal structure: even if it is an amorphous material (no structure arrangement at the atomic level), there is an organization at the nanometer to micrometer level. Amorphous opal might present an organized network of spheres (such as the one shown below). It is the existence of this network of silica spheres that enables diffraction of the light, following Bragg's law: nλ = 2dηsinθ where n is the order of diffraction, λ is the wavelength of the incident light,d is the network spacing, η the index of refraction of opal, and θ the angle of the diffracted light with the network. n (=1), η (=1.45) and λ (=390 to 780 nm for the light the our eyes can see) are fixed, so only the size of the spheres and the angle of the incident light have an influence. That is why the color changes when moving a play-of-color opal (or when the observer moves relatively to the opal).
Pleochroism is an optical property observed in certain minerals in which light is absorbed differently as it passes through the crystal in different directions. Differences in the internal arrangement of atoms in the crystal in different directions account for the differential light absorption. Three distinct colors (trichroism) or two distinct colors (dichroism) may be seen as a crystal is held in front of a light and turned.