GALENA WITH QUARTZ
A spectacular specimen of Galena with Quartz. Featuring large cubic Galena crystals clustered together and covered with perfect little quartz crystals and tiny Galena cubes on top. The term “Ay Carumba” springs to mind! This amazing piece even has some iridescence and the underside has further interesting Galena formations. A super piece that will grace any collection. A one-of-a-kind find for the serious collector.
10.5cm x 10cm x 4.5cm, 1372g.
Largest crystal face approx. 4cm square.
Krushev Dol Mine, Madan, Bulgaria
GALENA Lead Sulfide PbS is a common and popular mineral for rock hounds. Its characteristic cubes, distinctive cleavage and high density make it easy to identify and a favorite in high school geology labs. The structure of Galena is identical to that of halite, NaCl. The two minerals have the same crystal shapes, symmetry and cleavage. Some Galena may contain up to 20% silver. Galena is the leading ore of Silver.
Is the primary ore mineral of lead. Worked for its lead content as early as 3000 BC, it is found in ore veins with sphalerite, pyrite, chalcopyrite, tennantite-tetrahedrite, etc. and in skarns, as well as in sedimentary rocks where it may replace carbonate beds or be deposited in pore spaces. The crystals are bright when fresh but often tarnish after exposure to air and especially when people touch it. Lead sulfide may contain impurities, such as silver, arsenic, antimony, and copper.
One of the first transistors was a Galena Crystal and with a copper wire called “cats-whisker-with crystal”. Galena is a natural semiconductor. Really it formed part of a transistor, a more reliable PN junction or Diode. Metal Sulfides were experimented with in the late 1800s and early 1900s as they form natural PN Junctions like copper and copper oxide (Verde or Patina) which also formed one of the first solar panels. Such an interesting subject I could on on about it.
There are many forms of Galena specimens. Cubic Crystal, Octahedron Crystal, Cuboctahedron or Octacube, Truncated, Skeletal, Melted, Wet look and more.
Color is lead to silver gray sometimes with a bluish tint.
Luster is metallic to dull in weathered faces.
Transparency crystals are opaque.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include the cube, octahedron and combinations of the two. Spinel twinning is possible forming flattened crystals. Also massive and granular.
Cleavage is perfect in four direction forming cubes.
Fracture is uneven and rarely seen because of the perfect cleavage.
Hardness is 2.5+
Specific Gravity is approximately 7.5+ (heavy even for metallic minerals)
Streak is lead gray
Chemistry PbS, Lead Sulfide
Uses Major ore of lead and silver, Specimens, previously Plumbing pipes and Paint. It is toxic when ingested or inhaled.
Brighter metallic luster on cleavage surfaces than on crystal faces.
Notable occurrences include Texas-Oklahoma-Missouri area, USA; Germany, Peru, Mexico, Zambia, and England.
Best Field Indicators are crystal habit, cleavage and, perhaps most importantly, density.
Associated Minerals are Cerussite, Anglesite, Quartz, Sphalerite, Chalcopyrite, Pyrite, Bornite, Barite, Siderite, Dolomite, Calcite, Marcasite, Fluorite and then some.
Quartz Sample Images
Quartz is a fascinating common mineral, found in the Earth’s crust. If pure, quartz forms colourless, transparent hard crystals with a glass like luster. A significant component of many igneous, metamorphic and sedimentary rocks. Found in an abundant variety of formations and colors.
Polished Quartz was the most advanced technology thousands of years ago, used by the Assyrians. As a lens to focus light, could help start a fire for cooking. The Vikings could have used one of these to find the sun on a cloudy day. As a magnifying glass the ancients could see the stars too. Today it leads technology being the main component of transistors which make our computers work and solar panels.
The presence of trace elements gives an abundance of color range and crystal forms. Quartz is hard 7, light 2.65 and just adorable with an amazing shine when polished. No cleavage, characteristic conchoidal fracture and strongly piezoelectric and pyroelectric. Interestingly except in Twins where the opposites cancel each other out.
Chemistry: SiO2 , Silicon dioxide
Uses: silica for glass, electrical components, optical lenses, abrasives, gemstones, ornamental stone, specimens, building stone, etc.
Variety specimens include.
Amethyst is the purple gemstone variety.
Citrine is the yellow to orange gemstone variety. It is rare in nature and often created by heating Amethyst.
Milky Quartz is the cloudy white variety.
Rock crystal is clear quartz and used as a gemstone.
Rose quartz is a pink to reddish pink variety.
Smoky quartz is the brown to gray variety.
Clear quartz is the most common color then white or cloudy milky quartz. Purple (Amethyst), pink (Rose Quartz), gray or brown to black (Smoky Quartz) are also common.
Luster is glassy to vitreous as crystals, while cryptocrystalline forms are usually waxy to dull but can be vitreous.
Transparency: Crystals are transparent to translucent, cryptocrystalline forms can be translucent or opaque.
Crystal System is trigonal; 3 2.
Crystal Habits are again widely variable. A prominent habit is hexagonal prisms, terminated with a six sided pyramid. This is two rhombohedrons. Three of the six sides of the pyramid may dominate causing the pyramid to be or look three sided. Left and right handed crystals are possible and identifiable only if minor trigonal pyramidal faces are present. Druse forms (crystal lined rock with just the pyramids showing) are also common. Massive forms can be just about any type but common forms include botryoidal, globular, stalactitic, agate.
Cleavage is very weak in three directions (rhombohedral).
Fracture is conchoidal.
Hardness is 7, less in cryptocrystalline forms.
Specific Gravity is 2.65 or less if cryptocrystalline. (average)
Streak is white.
Other Characteristics: Striations on prism faces run perpendicular to C axis, piezoelectric (see tourmaline) and index of refraction is 1.55.
Associated Minerals are numerous and varied but here are some of the more classic associations of quartz. Amazonite a variety of microcline, tourmalines especially elbaite, wolframite. But wait there’s more pyrite, rutile, zeolites, fluorite, calcite, gold, muscovite, topaz, beryl, hematite and spodumene.
Notable Occurrences of amethyst are Brazil, Uraguay, Mexico, Russia, Thunder Bay area of Canada, and some locallities in the USA. For Smoky Quartz; Brazil, Colorado, Scotland, Swiss Alps among many others. Fine examples of Rock crystal come from Brazil, Arkansas, many localities in Africa. Fine Agates come from Brazil, Lake Superior, Montana, Mexico and Germany.
Best Field Indicators are first the fact that it is very common. Then crystal habit, hardness, striations, good conchoidal fracture and lack of good cleavage. Assume transparent clear crystals may be quartz.