Discussion: Botryoidals

Category: Discussion Forum / 6--Geology/Rock & Mineral Identification

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gamaliel114	Botryoidals Sep 25 2009, 5:54 PM EDT I guess this is directed toward Bill. What is your understanding of why certain minerals adopt the botryoidal habit? That is, do we know what conditions must be present for the crystals to form in that manner? ~Zeke Post reply Do you find this valuable? Keyword tags: botryoidal crystals greywacke jade nephrite
aubreyreynolds9@gmai	1. RE: Botryoidals Sep 25 2009, 8:17 PM EDT \| Post edited: Sep 25 2009, 9:09 PM EDT Crystallography is one of the most difficult courses I took in college. I was in charge of the crystallizers at Reynolds Metal. What you asked is not an easy question but I will give it a try. It takes a little chemistry to understand the phenomena of Botryoidal habit. In chemistry and mineralogy, a crystal is defined as a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern that extends in all three spatial dimensions. Minerals will form crystals depending on the type of molecule that make up the mineral and the environmental conditions . Quartz crystals (Silicon Dioxide SiO2) are commonly seen in the hexagonal prisms. (Six sided crystals), Silicon Dioxide is the base molecule of a wide variety of gemstones: amethyst, citrine, jasper , agate and many more. If you looked at agates under a microscope you would see very small crystals. In Fact the size of the crystals vary depending on whether it is a band or the space between bands, Between bands have larger crystals that can often be seen with the naked eye. If the agate is hollow large crystal points are often seen lining the space. But this is not the only habits that quartz occurs, In fact most minerals occur more commonly in other habits than the well known crystals.. The botryoidal habit is also frequently seen in minerals formed under near surface conditions in a low temperature environment. Quartz often occurs in the Botryoidal habit. Botryoidal means grape like so this formation looks like bumps or clusters of grapes. Now the basic question. Why spheres? Here is the simple explanation. Molecules organize themselves to pack the space depending on their structure. Salt crystals are cubes, If you look at the crystal under a microscope you will see tiny cubes. Post reply 5 out of 5 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	2. RE: Botryoidals Sep 25 2009, 8:45 PM EDT \| Post edited: Sep 25 2009, 8:56 PM EDT Increase the magnification you will see smaller cubes, Cubes neatly fill the space. No gapes. Crystals grow from super saturated water solutions. Just like the solution grown crystals that you might have been given as a child as a present. Mix with water and watch the crystals grow. You can grow salt crystals the same way. Mix with hot water until you can not add any more salt (saturated) and let it cool. It becomes super saturated. Bingo - crystals of salt. The formation of solid crystals from a homogeneous solution consists of two major stages: nucleation and crystal growth. A small nucleus slowly builds molecule upon molecule until a large crystal forms. Under the right conditions of slow growth; crystals can become huge like the selenite crystals in Mexico or the 1000 pound quartz crystal I posted. Now imagine a low temperature solution that is supersaturated. The tiny nuclei are scrambling to pack together but the conditions will not allow them to slowly form large crystals. They are compelled to fit into a space that has the the lowest surface tension. A rounded surface or a complete ball. Think of calcite in a cave. The cool saturated solution grows rounded formations like cave corals or other unique shapes that are not the classic calcite crystal. I did a study for Reynolds where I grew Aluminum Oxide crystals. I saw the same thing/ Slow growth-- well shaped crystals. More rapid growth --- rounded surfaces and nuclei clumped together. In nature growth is much slower than in a laboratory. I hope I did not muddy the water. Summary: 1,Crystals grow from water solutions with dissolved minerals. 2, The conditions of temperature and pressure determine the habit the mineral will take. 3, Large crystals (seen with the naked eye) require a slower more ordered growth. Post reply 4 out of 4 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	3. RE: Botryoidals Sep 25 2009, 9:07 PM EDT Volcanic rock is a good example of a similar phenomena. Igneous rock that slowly cools deep within the earth has time for crystals to grow, Pick up a piece of granite which cooled very slowly and you can easily see crystals often quartz, mica and feldspar. On the other hand have you seen lava flow into the ocean. What shapes forms -- Rounded masses. Post reply 4 out of 4 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	4. RE: Botryoidals Sep 25 2009, 9:26 PM EDT \| Post edited: Sep 25 2009, 9:30 PM EDT Rock Candy is a great science lesson in how crystals grow. Here is a recipe I found for the kids and grand kids. Help them out grand paw. ROCK CANDY Ingredients * 6 cups cold water * 6 cups white sugar * food coloring (if desired) Directions Thoroughly wash and rinse a 2 quart jar. In a large pan, pour all water. Heat to near boiling and add sugar, one cup at a time, stirring well between additions, until completely dissolved. If you desire colored candy, add your coloring now. Pour sugar water into jar and place a string(s) in the jar, making sure to tie it to a stick that spans the top of the jar. Cover with a cloth, to keep out dust, and let rest until crystals have formed on the skewer, up to 2 weeks. Cook's Notes- if you desire a candy with larger crystals, you will want to "seed" your string. Wet the string and roll it in sugar before placing it in the sugar water. Be sure not to disturb the crystals as they are growing. Do not touch the jar. Post reply 4 out of 4 found this valuable. Do you find this valuable? Do you?
gamaliel114	5. RE: Botryoidals Sep 25 2009, 10:01 PM EDT Thanks Bill. That is the best explanation I've found. I think you confirmed why and where to find the botryoidal jades. It's an area where a reaction zone developes (near surface compared with the bulk of the serpentinite mass). Temps are lower or are lowered by the metasomatic chemical exchanges. They must be cooling rapidly because I have never found any crystals even though the solution is primed for them (particularly garnets). Still have to figure out at which point in the series they are likely to be found. I'll be checking an area next week, and I'll see if I can't decifer an answer from the literature on those zones. ~Zeke Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	6. RE: Botryoidals Sep 25 2009, 10:32 PM EDT "Thanks Bill. That is the best explanation I've found. I think you confirmed why and where to find the botryoidal jades. It's an area where a reaction zone developes (near surface compared with the bulk of the serpentinite mass). Temps are lower or are lowered by the metasomatic chemical exchanges. They must be cooling rapidly because I have never found any crystals even though the solution is primed for them (particularly garnets). Still have to figure out at which point in the series they are likely to be found. I'll be checking an area next week, and I'll see if I can't decifer an answer from the literature on those zones. ~Zeke" That's right. Botryoidal masses would be a a closer to the surface phenomena than a deep earth process. I would expect botryodal jade to be closer to the surface or in vugs, Bill Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	7. RE: Botryoidals Sep 26 2009, 9:00 AM EDT \| Post edited: Sep 26 2009, 10:09 AM EDT Now we are talking Jade I should have know. Nephrite is a variety of the calcium and magnesium-rich amphibole mineral actinolite (aggregates of which also make up one form of asbestos). The chemical formula for nephrite is a2(Mg,Fe)5Si8O22(OH)2.[1] It is one of two different mineral species called jade. The other mineral species known as jade is jadeite, which is a variety of pyroxene. While nephrite jade possess mainly grays and greens (and occasionally yellows, browns or whites), Jadeite jade, which is rarer, can also contain blacks, reds, pinks and violets. Nephrite jade is an ornamental stone, used in carvings, beads, or cabochon cut gemstones. I posted this not so much for you Zeke, You are our resident Jade expect but for others not familiar with Nephrite. The following is a link to an article on crystal growth in Nephrite. Great electron microscope pictures of the micro crystalline structure of jade. The interlocking crystals give the mineral great toughness. http://www.minersoc.org/pages/Archive-MM/Volume_49/49-350-31.pdf Bill Post reply 4 out of 4 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	8. RE: Botryoidals Sep 26 2009, 9:50 AM EDT \| Post edited: Sep 26 2009, 10:08 AM EDT There is a great deal of evidence that the deposits of jade in the Northwest are a result of the metamorphic process by which minerals of a rock or ore body are replaced by minerals of a different chemical composition as a result of the action of a fluid, esp. of moving water. Botryoidal jade often contain pseudomorphs; clear evidence of mineral replacement. Some Nephrite jade is a result of metasomatism of silicic rocks in serpentinite (or serpentinite melange) by Ca-Mg-rich fluids or a boundary reaction/infiltration of silicic rocks or fluids acting upon antigorite serpentinite and serpentinite fluids, According to a paper by HARLOW, G. E. and SORENSEN, S. S. of the Smithsonian Institution, Botryoidal nephrite from northern California appears to result from infiltration of serpentinite vein fluid into permeable graywacke blocks, reaction with the permeable matrix, and creation of little “cumulus cloud” structures. The conclusions we reached for the botryoidal jade appear to be backed up by published papers. I enjoy discussing science. Post reply 4 out of 4 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	9. RE: Botryoidals Sep 26 2009, 10:17 AM EDT Based upon the HARLOW paper you should be looking for deposits of graywache blocks as the host rock for the botryoidal jade. Graywache is a sedimentary rock composed of sand-sized grains in a fine-grained clay matrix. The sand-sized grains frequently include rock fragments of wide-ranging mineralogies (e.g., pyroxenes, amphiboles, feldspars, and quartz). The clay matrix may constitute up to 50% of the volume. Of the clay minerals, chlorite and biotite are most abundant. The matrix tends to bind the grains strongly and form a relatively hard rock. Bill Post reply 3 out of 3 found this valuable. Do you find this valuable? Do you?
jakesrocks	10. RE: Botryoidals Sep 26 2009, 10:22 AM EDT Great info Bill. Makes my head hurt, reading all of this scientific stuff, but great info non-the -less. Keep it coming. Maybe you can teach some of us old timers a thing or two. Don Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	11. RE: Botryoidals Sep 26 2009, 10:31 AM EDT \| Post edited: Sep 26 2009, 10:33 AM EDT Another paper states that in the geographical center of the State of Washington green nephrite are examples of almost pure thermal metamorphism of inter bedded graywackes, Graywacke adjacent to the serpentine was weakly metamorphosed to a nephrite. Bill Post reply 3 out of 3 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	12. RE: Botryoidals Sep 26 2009, 10:38 AM EDT Don this sounds a lot like the formation of botryoidal agates (bubble gum agates) of SD except for the minerals involved. Of course the Bubble Gums are chalcedony (Silica). The process is similar. Thanks for your encouragement. I love science but I do not want to bore folks. Bill Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
jakesrocks	13. RE: Botryoidals Sep 26 2009, 10:42 AM EDT "Don this sounds a lot like the formation of botryoidal agates (bubble gum agates) of SD except for the minerals involved. Of course the Bubble Gums are chalcedony (Silica). The process is similar. Thanks for your encouragement. I love science but I do not want to bore folks. Bill" Man Bill, this is anything but boring. I could spend the whole day reading about rocks and minerals, and how they were formed. Don Post reply Do you find this valuable?
aubreyreynolds9@gmai	14. RE: Botryoidals Sep 26 2009, 12:51 PM EDT "Man Bill, this is anything but boring. I could spend the whole day reading about rocks and minerals, and how they were formed. Don" I am going to make my grandchildren some rock candy from the above recipe. Is anyone going prospecting this weekend. There are so many motor cycles on the road for Bike, Blues and BBQ rally that it is difficult to drive, Bill Bill Post reply Do you find this valuable?
jakesrocks	15. RE: Botryoidals Sep 26 2009, 1:09 PM EDT Great idea Bill. I haven't made that stuff in many years. The wife is gone for the day, and she bought a fresh bag of sugar yesterday. Hmmm ! Don Post reply Do you find this valuable?
rockcandyguy	16. RE: Botryoidals Sep 27 2009, 12:58 AM EDT \| Post edited: Sep 27 2009, 11:37 AM EDT HI Bill, great info in this thread! At Rock Candy, both fluorite and quartz occur in botryoidal habit. The hemispherical quartz always starts as sub-parallel needles, which under magnification look like a pin cushion. The prism faces are elongated to an amazing aspect ratio, 50:1 or more, so in hand specimen the crystals appear fibrous. Individual hemispheres occur to 2 inches across. The botryoidal fluorite is an assemblage of cube faces, each sligtly rotated from the axis of the original cube. Sunagawa, in his book "Crystals: Growth, Morphology, and Perfection" (Cambridge, 2005), says such rotation starts as step dislocation on a molecular level. The curious thing to me is that the offsets appear to be random to produce a hemispherical surface. BTW, neither of these examples formed at low temperatures ... the veins at RC are pulsed hydrothermal, and were hot enough to alter the syenite footwall a dozen feet from the vein. Perhaps there is more than one method of botryoidal formation? I'll get back to this discussion next time I'm out of the hills. Bob Bob Post reply 2 out of 2 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	17. RE: Botryoidals Sep 27 2009, 9:39 AM EDT "I guess this is directed toward Bill. What is your understanding of why certain minerals adopt the botryoidal habit? That is, do we know what conditions must be present for the crystals to form in that manner? ~Zeke" Zeke have you found any more Botryoidal jade? Bill Post reply Do you find this valuable?
pvjjh	18. RE: Botryoidals Sep 27 2009, 1:27 PM EDT "Another paper states that in the geographical center of the State of Washington green nephrite are examples of almost pure thermal metamorphism of inter bedded graywackes, Graywacke adjacent to the serpentine was weakly metamorphosed to a nephrite. Bill" Interesting Bill. What is the name of the paper as I live fairly close to the geographic center of the state and kind of curious the paper. I have never heard of anything like this close around here. Way cool. Paul Post reply Do you find this valuable?
pvjjh	19. RE: Botryoidals Sep 27 2009, 1:31 PM EDT "Don this sounds a lot like the formation of botryoidal agates (bubble gum agates) of SD except for the minerals involved. Of course the Bubble Gums are chalcedony (Silica). The process is similar. Thanks for your encouragement. I love science but I do not want to bore folks. Bill" I often wondered about the formation of such agates. I am assuming the fire agate I have are all formed in this manner since the all look like bubbles - at least the material I have. Great info! :-) Paul Post reply Do you find this valuable?

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Discussion: Botryoidals

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