liftedanew 1 Posted June 3, 2019 Share Posted June 3, 2019 Looks Jaspagate, has Actinole. Also totally translucent. Thinking petrified wood, like a Mexican fire Opal. Problem is seems too tough to be Opal. Any ideas? 1 Quote Link to post Share on other sites
Bedrock Bob 3,871 Posted June 3, 2019 Share Posted June 3, 2019 That is quartz. Agate, jasper and opal are cryptocrystalline and have poor to no cleavage. You can plainly see the crystals structure of your specimen as well as the strong cleavage between those crystals. It is macrocrystalline. Look at how it breaks and how the fractures follow cleavage lines. Now hit it with a hammer and break off a piece. You will see the surface follows little crystals like a salt block or sugar cube. Jaspers, agates and opals are glassy and follow stress lines through a mass with no cleavage and leave smooth conchoidal fractures. If it is sugary it is quartz. If it is translucent and flinty it is agate. If it is opaque and flinty it is jasper. If it is glassy and has long conchoidal fractures it is opal. Opal and obsidian are distinctly different from jaspers and agates by virtue of the way they form and their "toughness" and are more like glass than a stone. They are all silicon dioxide but have subtly different physical characteristics. The crystal habit, hardness and appearance will become more familiar to you as you learn to identify the silicates. 3 Quote Link to post Share on other sites
liftedanew 1 Posted June 3, 2019 Author Share Posted June 3, 2019 Quartz red and yellow with the white quartz zones? Very intriguing. Y is this piece translucent? Light penetrates fully to other side. Like a Moonstone. Sugar lamp types u mean by sugary? Sugary quartz is something real? Hold up I be back. Quote Link to post Share on other sites
Bedrock Bob 3,871 Posted June 3, 2019 Share Posted June 3, 2019 It is translucent because light penetrates it. That is the definition of translucent. Many silicates are translucent and this is obviously a silicate. Yes, moonstones are one of many minerals that can be translucent. But not all moonstones are translucent and not all translucent minerals are moonstones. Moonstones are a group of feldspars that show a play of light at certain angles. They have a completely different crystal habit from your specimen and your specimen will not show a play of light. By sugary I mean the crystal texture of the mineral. Jasper, agate and opal have crystals so tiny you need high power magnification to see. Your specimen has clearly defined crystals visible to the naked eye. It is granular. This means it was formed under some pressure and is crystalline quartz. Cryptocrystalline minerals like agate, jasper and opal were formed near the surface at zero pressure. They are not granular like a salt block or sugar cube. They are glassy and without cleavage or visible crystals. Get yourself a copy of the Audubon Field Guide to Rocks and Minerals and learn about the silicate minerals and how crystal habit, fracture and cleavage play together. Internalize the fact that the larger the crystals the more pressure the mineral formed under (and the inverse as well). Get some specimens of common opal, agate and jasper and quartz and hit them together and break them up with a hammer. Once you familiarize yourself with the physical characteristics of these chemically related materials identification will be a lot easier. 3 Quote Link to post Share on other sites
d_day 307 Posted June 3, 2019 Share Posted June 3, 2019 Quartzite. 2 Quote Link to post Share on other sites
Bedrock Bob 3,871 Posted June 4, 2019 Share Posted June 4, 2019 16 hours ago, d_day said: Quartzite. liftedanew, This is an excellent point. The specimen is comprised of the mineral quartz. The rock is called quartzite. Rocks are made up of minerals. In order to identify a rock one must identify the minerals that it is comprised of. Some rocks are made up of many minerals and some are made from just one. In this case the name of the mineral and the name of the rock are similar and that can be confusing. Many novices don't grasp this point. Rock identification and mineral identification are two different but interrelated things. I have identified the mineral that the specimen is comprised of as quartz. d_day has identified the rock as quartzite. Both are accurate. It is important to grasp the difference in what we are describing. 2 Quote Link to post Share on other sites
4meter 186 Posted June 4, 2019 Share Posted June 4, 2019 There is dark green and purple minerals in there as well. What is it now? Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.