The Del Air Rockhounds Club Welcomes You!!

The Del Air Rockhounds Club was founded in 1952 with members mostly residing in the San Fernando Valley area of California. Our club is a non-profit organization dedicated to sharing knowledge of the lapidary arts and techniques, geology, mineralogy and related fields. We own our own lapidary equipment with members available to teach and demonstrate lapidary techniques to other members.

Our members enjoy lapidary related programs, demonstrations, exhibitions, displays and lectures.

We also take monthly field trips to our local deserts and mountains for exploration and the study and collection of lapidary specimens.

November 2009 Mineral of the Month

PYROMORPHITE

Named in 1813 from the Greek for "fire" and "form" because after being melted into a globule a sample will begin to take on a crystalline shape during cooling.

Pyromorphite is a secondary lead mineral found in the oxidized zones of lead deposits. Typically found as green, yellowish, brownish, greyish or white barrel-shaped hexagonal prisms, in clusters or as druses on matrix. The individual crystals are often modified or etched, giving a hopper-like appearance. This lead chloride phosphate forms a complete series with mimetite and vanadinite.

Pyromorphite is a member of the phosphates group and comes in at 3-1/2 to 4 on the Mohs Scale. It has a hexagonal crystal system with a resinous luster. It is transparent to translucent with a brittle tenacity and indistinct cleavage. Its fracture is irregular and uneven. Its chemical composition is Pb5(PO4)3CI. Its specific gravity is 6.5 to 7.1

Pyromorphite can commonly form pseudomorphs after Galena and Cerussite. There are no commercial uses for this mineral other than providing dazzling display specimens for collectors worldwide.

October 2009 Mineral of the Month

BENITOITE

Benitoite was first described in 1907 by George D. Louderback, who named it benitoite. "as it occurs near the head waters of the San Benito River in San Benito County, California." It is the California State gemstone.

Benitoite is a rare blue barium titanium silicate mineral found in hydrothermally altered serpentinite and also in schists. Benitoite fluoresces under short wave ultraviolet light, appearing light blue in color.

Benitoite is a member of the silicates group. It comes in at a 6-6-1/2 on the Mohs Scale. It has a conchoidal to uneven fracture and an indistinct cleavage. It has a trigonal/hexagonal crystal system with a vitreous luster. Benitoite is typically blue, purple, pink, white, colorless and often multicolored. The stone is transparent to translucent with a colorless streak. Its chemical composition is BaT1Si3O9.

Benitoite is typically found with some combination of natrolite, joaquinite and neptunite on a greenish-gray serpentinite base.

Benitoites' main uses are as collectors' specimens, especially in specimens which show off its commonly associated minerals. Benitoites' hardness also makes it suitable for use as a gemstone, though the general lack of suitable material has limited this use.

September 2009 Mineral of the Month

AZURITE

Its name comes from the Persian word 'Lazhward', meaning 'blue', in reference to its color.

There are over 45 well-known forms, and over 100 forms have been described. Azurite is often pseudomorphed to Malachite, and the two are very frequently found together.
It is a member of the carbonates group and its chemical composition is Cu3+2(CO3)2(OH)2.
It has a perfect cleavage and has a conchoidal fracture. It is a very soft stone coming in at 3-1/2 to 4 on the Mohs Scale. Its specific gravity is 3.77 to 3.78.
This mineral's typical crystal system is monoclinic. It forms as tabular and short prismatic crystals which may be twinned. It also occurs in massive, nodular, stalactitic and earthy habits.
It is usually a rich deep azure blue. The streak is a paler blue. Azurite varies from transparent to opaque and it has a vitreous or dull luster.
Azurite forms in the oxidized regions of copper deposits. It is a secondary mineral formed by the action of carbonated water acting on copper-containing minerals
Azurite is soluable in hydrochloric acid with effervescence. It fuses easily and will turn black when heated.
The intense color of Aurite makes it a popular collector's stone. However, bright light, heat, and open air all tend to reduce the intensity of its color over time. To help preserve the deep blue color of a pristine Azurite specimen, collectors should use a cool, dark, sealed storage environment similar to that of its original natural setting.
Azurite was used as a blue pigment for centuries. Depending on the degree of fineness to which it was ground, and its basic content of copper carbonate, it gave way to a wide range of blue hues.

July 2009 'Specimen' of the Month

Hello All, This month, in honor of our July program, we will be changing our mineral of the month to our 'Specimen of the Month'.........................."STROMATOLITES"

'STROMATOLITES'

Stromatolites are not only Earth's oldest of fossils, but are intriguing in that they are our singular visual portal into deep time on earth, the emergence of life, and the evolving of the beautiful forms of life of modern time. A small piece of stromatolites encodes biological activity perhaps spanning thousands of years. In broad terms, stromatolites are fossil evidence of the prokaryotic life that remains today, as it has always been, the preponderance of biomass in the biosphere. For those that subscribe to the theory of the living earth, it is the prokaryotes that maintain the homeostasis of the earth, rendering the biosphere habitable for all other life. They maintain and recycle the atomic ingredients of which proteins, the essence of life, are made, including oxygen, nitrogen and carbon. We humans are, in simple terms, bags of water filled with proteins and prokaryotic bacteria (the bacteria in your body outnumber the cells in your body about 10 to 1). We humans have descended from organisms that adapted to living in a prokaryotic world, and we humans retain (conserved in evolutionary terms) in our mitochondria the cellular machinery to power our cells that we inherited from the prokaryotes of deep time on earth.

Scientists disagree on how to define stromatolites. A common definition goes something like: A lamiated rock formed by the growth of blue-green algae (i.e., cyanobacteria)". This definition is, in fact, such a gross oversimplification as be scientifically useless. It does contain a modicum of truth, however, in that the largest volume of stromatolite formations was likely formed by biogenic processes involving photosynthetic cyanobacteria. Cyanobacteria’s metabolic byproduct, oxygen, rusted the earth, pumped enormous oxygen poison to them into earth’s atmosphere, and in so doing paved the way for aerobic-based life to emerge and diversify; cyanobacteria’s contributions to life led to their own prodigious decline.

Stromatolites and their close cousins the thrombolites, are rock-like buildups of microbial mats that form in limestone- or dolostone-forming environments. Together with oncoids (formerly called "algal biscuits" or "Girvanella"), they typically form by the baffling, trapping, and precipitation of particles by communities of microorganisms such as bacteria and algae. In some cases, they can form inorganically, for example when seawaters are oversaturated with certains chemicals resulting in precipitation. Stromatolites are defined as laminated accretionary structures that have synoptic relief (i.e., they stick up above the seafloor). Stromatolite-building communities include the oldest known fossils, dating back some 3.5 billion years when the environments of Earth were too hostile to support life as we know it today. We can presume that the microbial communities consisted of complex consortia of species with diverse metabolic needs, and that competition for resources and differing motility among them created the intricate structures we observe in these ancient fossils. Microbial communities diversified through time, with eukaryotic organisms eventually joining the mix.

Excluding some exceedingly rare Precambrian fossils such as the Ediacaran fauna, stromatolites and are the only fossils encoding the first 7/8th of the history of life on earth. They encode the role that ancient microorganisms played in the evolution of life on earth and in shaping earth's environments. The fossil record of stromatolites is astonishingly extensive, spanning some four billion years of geological history with the forming organisms possibly having occupied every conceivable environment that ever existed on earth. Today, stromatolites are nearly extinct in marine environments, living a precarious existence in only a few localities worldwide. Modern stromatolites were first discovered in Shark Bay, Australia in 1956, and throughout western Australia in both marine and non-marine environments. New stromatolite localities have continued to be discovered in various places such as the Bahamas, the Indian Ocean and Yellowstone National Park, to name but a few localities.