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 & mountains for exploration and the study and collection of lapidary and mineral specimens.

May 2012 Rock of the Month

Meteorites & Tektites

 

A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. A meteorite's size can range from small to extremely large. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids. When a meteoroid enters the atmosphere frictional, pressure and chemical interactions with the atmospheric gasses cause the body to heat up and emit light thus forming a fireball, also known as a meteor or shooting star. The term bolide refers to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface. As of February 2010, there are approximately 1,086 witnessed falls having specimens in the world's collections. In contrast, there are over 38,660 well-documented meteorite finds. Meteorites have 

traditionally been divided into three broad categories: stony meteorites are rocks, mainly composed of silicate minerals; iron meteorites are largely composed of metallic iron-nickel; and, stony-iron meteorites contain large amounts of both metallic and rocky material.

Tektites are natural glass rocks up to a few centimeters in size, which most scientists argue were formed by the impact of large meteorites on Earth's surface. Tektites are typically black or olive-green, and their shape varies from rounded to irregular. Tektites are among the "driest" rocks, with an average water content of 0.005%. This is very unusual, as most, if not all, of the craters where tektites may have formed were underwater before impact. Also, partially melted zircons have been discovered inside a handful of tektites. This, along with the water content suggests that the tektites were formed under phenomenal temperature and pressure not normally found on the surface of the Earth.

May 2012 Program

Larry Bradbury, Meteorite Man

Our special guest this month will be Mr. Larry Bradbury. He will be speaking on a very interesting subject: Meteorites (Rocks from Space). He will bring many of his collection pieces to the club meeting on Thursday May 3, 2012 @ 7:30 pm and will answer all your questions about meteorites. You don't want to miss this!

REGULAR MEETINGS ARE HELD ON THE 1ST THURSDAY OF EACH MONTH @ 7:30 PM AT:

NORTHRIDGE UNITED METHODIST CHURCH-9650 RESEDA BL. NORTHRIDGE, CA 91324

Guests are always welcome at our meetings and events

April 2012 Rock of the Month

      Limestone

 

 Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera, which is a species of marine plankton. Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses, including as building material, as aggregate to form the base of roads, as white pigment or filler in products such as toothpaste or paints, and as a chemical feedstock. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble.