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Let's Rock => Mineral Specimens => Topic started by: Kaljaia on September 23, 2018, 10:21:49 AM
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I thought it would be a fun project to see how many different types of agate I can find from a single location :P make up a little ID chart for the place. I'm still putting together the list. Here's what I have so far:
Dendritic
(https://78.media.tumblr.com/1acaacf3f6432e789a43dbffc4da221c/tumblr_pfiqo1a58j1vg3vluo1_1280.jpg)
Banded
(https://78.media.tumblr.com/a9d684d37adeda89f3b294f44c2820fc/tumblr_pfiqo1a58j1vg3vluo2_1280.jpg)
T-egg core
(https://78.media.tumblr.com/f633c1521e0cd6de4a2ec9f5fb0e062b/tumblr_pfiqo1a58j1vg3vluo3_1280.jpg)
Flame agate
(https://78.media.tumblr.com/eaa5d1378c9661d74882522a10b8a705/tumblr_pfiqo1a58j1vg3vluo4_1280.jpg)
Agate geode
(https://78.media.tumblr.com/0b42aa509f39a02c6c571bc9c5390f1f/tumblr_pfiqo1a58j1vg3vluo5_1280.jpg)
Moss agate
(https://78.media.tumblr.com/8c0ef12bc44147d8d7851c4570e36d05/tumblr_pfiqo1a58j1vg3vluo6_1280.jpg)
Waterline agate
(https://78.media.tumblr.com/5f86e427c601a9c3a77192327476d0ad/tumblr_pfiqo1a58j1vg3vluo7_1280.jpg)
Botryoidal agate
(https://78.media.tumblr.com/8b1f824f1e02cd4fb7a45d14749351e9/tumblr_pfiqo1a58j1vg3vluo8_1280.jpg)
I have tube agate and one small piece of plume too, not photographed yet. Any others I'm missing? I'm hoping to make a easy-to-use key for the local kids and will be improving the photographs after I put the set together.
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Nice variety. Is banded a banded and or Fortification Agate?
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Nice variety. Is banded a banded and or Fortification Agate?
I'm not firm on the difference between the two, honestly. Is it a difference in appearance or formation? I've been using the terms interchangeably but if they are two separate materials I'd love to learn more!
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This is how I have always understood it. Although fortification is almost always banded, banded is not always fortification. Fortification refers to concentric bands around a central point (like walls around a fort, hence the name fortification). Banded agates may have bands of differing shapes and sizes that wander to and fro but never create a fortification effect. Your agate above I would classify as fortification agate, but banded would technically be a correct description for it as well.
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In addition to the fortified (resembling the plan of a 17th or 18th century fort) and non-fortified (wavy type banding), I've incorporated those mentioned with some other types that come to mind:
BANDED
· fortified (bands enclose a large area, resembling the floor plan of a 17th or 18th century fort);
· plain banded (a pattern of wavy lines);
· lace (lots of enclosed bands);
PATTERN
· dendritic (tree or shrub-like branching formations);
· plume (ostrich feather-like formations);
· moss (thread-like formations);
· picture, landscape or scenic (combination of patterns that resemble landscape paintings);
· orbicular or eye (contain ball-like inclusions);
· poppy agates (I'd include the so-called "Ocean Jasper" and some translucent poppy-type jaspers as agates);
· cloud (very soft, fuzzy bands and swirls);
· flame (fire-like plumes);
· waterline or onyx (parallel horizontal banding);
· Fischer (an artificially induced dendrite-type formation);
OPTICAL PHENOMENA
· iris (very, very tight banding that breaks light into a rainbow spectrum when backlit)
· fire (botryoidal formations containing thin layers of iridescent goethite and/or limonite);
· parallax or "shadow" (banding in transparent agate that gives a 3D effect);
· turtleback (botryoidal formation with very fine/invisible banding that forms a turtleshell type pattern when backlit);
FORMATION
· geode (a roundish thunderegg, vesicular agate or similar with a hollow center);
· thunderegg (a rhyolite nodule in a volcanic flow in which a gas chamber later filled with agate, often under great pressure);
· botryoidal or grape (resembles a grape-like cluster of orbs);
· mammillary (resembles udders);
· enhydro (contains bubbles of ancient water);
· vein or seam banded (pattern follows the outline of the crack which held it);
· amygdular (roughly round agate or geode formed in gas bubbles within volcanic host rock);
· membrane (filled with broken bits of the initial banded layers);
· polyhedral (a type of agate replacement where the agate follows the form of a previously dissolved polygonal mineral crystal);
· polymorph (agate that has replaced another mineral);
· sagenic (agate containing sagenite-type needles);
· agate casts (limb, bone and similar casts of once-living organisms);
· oolitic (contains small orbs; orbs larger than 5mm are pisolites, rather than oolites);
· brecciated or shatter (fully formed agate that has shattered and then re-healed);
...probably more. And it probably should be mentioned that some agates are combinations of two or more of these features.