Mama’s Weekly Rock Facts – Tiger Iron

Tiger Iron Skulls!

Tiger Iron is an altered mixture of layered red jasper, hematite, and tiger eye used mostly for jewelry making and ornamental stone carvings.  There’s not a clear consensus on whether tiger iron is a sedimentary rock, metamorphosed japilite, banded iron formation, or both.  If sedimentary, then stromatolite films may have facilitated the layering of sediments to form the banding.  If metamorphic, tiger iron would form at plate subduction zones where a tectonic plates moves under another and sinks into the mantle.

By Amanda Rice, Resident Geologist, Mama’s Minerals

See Mama’s Minerals selection of Tiger Iron and Tiger Eye

 

Mama’s Weekly Rock Facts - Soapstone

Soapstone which is also known as steatite or soaprock is a type of metamorphic rock called talc schist.  It is largely composed of talc which is the softest mineral on the Moh’s Hardness Scale with a 1.  Soapstone is relatively soft and may feel soapy, waxy, and or greasy when touched, hence the name soapstone.  

Soapstone Rough Rock

Soapstone has been used for centuries as a medium for carving and even as a building material.  In locations where it is prevalent such as India and Brazil, soapstone was used to build temples and pave roads.  With its variety of colors in greens, browns, grays, and whites soapstone continues to be one of the most common carving materials.  

by Amanda Rice, Resident Geologist, Mama's Minerals

Lapidary Tips – Cabochon Polishing Tip

Lapidary Tips – Cabochon Polishing Tip by Dick Peterson, TG&MS  

About 15 or 20 years ago, when I was cutting a lot of Bertrandite, I ran into a problem I hadn’t seen before. I had been shaping and sanding and polishing a lot of cabs when I had one that wouldn’t polish. The stone was a deep dark purple, one that I though would be outstanding. I went back to my Genie and re-sanded it and tried polishing it again. No luck. I set the cab aside and forgot about it.

Snowflake Obsidian 25mm Cabochon

            One day I was using some acetone and I spotted the cab so I cleaned it in the acetone. I then washed it in Dawn® Soap and warm water. Then I tried it again on the polishing wheel…it took a beautiful polish! What had happened during the cutting stage? It had been cut with oil and it had absorbed some oil. Oil is not a friend in cutting and polishing cabochons.

            If you suspect that the rock you are about to cut will absorb oil (some softer rocks do this) try the following before you cut it. Soak the rock in water for 24 hours or longer (longer is better). In the summertime put the container of the soft rock in the sun where it can warm up (the warmer the better). Keeping it warm helps the rock absorb more water. Next put the rock in the slab saw and cut it as soon as possible. The oil will slowly replace the water in the rock. Now is a good time to wash the slab with acetone. Anytime you cut slabs in your slab saw you should always place your slab in kitty litter (which is a great way to suck out the unwanted oil), wash your slab in warm soapy water. Dawn dish soap is one of the best to use.

By Dick Peterson; Timpanogos Gem & Mineral Society, Provo, UT

Rock Chips, December 2011