Preface to the series: Predecessors in the study of geology often compared minerals to words that interpret the earth, and the author often thinks about what kind of writing each mineral means. They should not all be serious scientific papers, but they should also have a romantic side that is close to our daily lives. This series of popular science hopes to introduce a variety of common minerals to you through literature/anecdotes, and establish a connection between minerals and life, science and poetry.
Poetic Mineralogy 5 –
Quartz: Travelogue
quartz
"Yes, I will come back on the waves.
Maybe death will hide me,
Silence will cover me,
But I will seek your understanding again,
My quest will not be in vain.
(Gibran, The Prophet)"
—Epigraph
If one of the most common minerals on the surface of the earth were to be selected, quartz (SiO2) would be the number one mineral – it can be found in the waves of the beach, in the crystalline clusters, in the soil (Figure 2), in jewelry, and ...... It can both dedicate itself and compose granite to make up the peaks of the Himalayas; It can also be compromised and precipitated by biological modification at the bottom of the ditch in Mariana. If you want to anthropomorphize minerals, quartz in the mountains, rivers, lakes and seas must be the "geologist" of minerals. Will it be like many geologists who love to explore, send tweets, write travelogues, and record their unforgettable journeys?
Fig.1 Sandy beach
Fig.2 Sandy soil
Scorching hometown
The most common quartz in the city may be translucent particles found in granite building materials (Fig. 3) and delicate ornaments made of crystal (clean and beautiful clusters of quartz crystals). These quartzes imprint the face of their homeland into their chemical composition: since the only elements that make up quartz are silicon and oxygen, it usually only occurs after the magma has undergone a differentiated evolution to reach silicon saturation. As a result, it is difficult to find traces of large-grained quartz in meteorites from small extraterrestrial bodies, and only planets as active as Earth are likely to form quartz above the centimeter scale through extensive and sustained magmatism. On top of that, only limited temperature and pressure conditions allow the quartz to grow sufficiently, cleanly and beautifully, and reach the quality of the gemstone (Fig. 4).
Fig.3 Granite building materials, translucent grease mineral is quartz
Fig.4 Gem-quality amethyst clusters
The careful quartz will not take the description of the hometown in one stroke, and more information is organized and stored by it, carefully hidden in its own trace element content. By measuring the titanium content in quartz and combining a variety of crystallographic parameters, scientists can deduce the temperature at which quartz crystallizes from magma. Regularly grown quartz also leaves behind ring-like rings of trees (Fig. 5), and with the help of an electron microscope, we can turn the pages of quartz's travelogue and imagine the hometown of quartz.
Fig.5 Growth rings of trees and rings of quartz under electron microscopy
Changeable adventures
Most of the quartz raw materials used in industry are quartzite formed by metamorphism (Fig. 6). They are either flattened and deformed by pressure, or reacted with melts to deteriorate, or metasomatized with fluids during geological adventures, and their properties are reset by changing geological processes. The adventurous journey requires compromise, as high pressure can cause the quartz to transform its crystal shape, fracture or reorient under the microscope (Figure 7); The addition of fluid can even cause the quartz to dissolve, drift to a new location and recrystallize.
Fig.6. Quartzite, quartz content > 90%
Fig.7. Quartz schist under the microscope,
The quartz (black, white, and gray in the picture) is arranged in a directional manner
In addition to the changes in appearance, the "voice of the heart" of quartz tells the story of travel in more detail—the lattice defects of quartz may contain some foreign substances, forming inclusions, and directly recording the "defects in the journey" (Fig. 8). By testing and analyzing the morphology, chemical composition and isotopic characteristics of inclusions in quartz, geological researchers can reverse the history it has experienced and get a glimpse of the geological secrets of mineralization.
Fig.8. Crystal of oil bile inclusions (top) and quartz inclusions under the microscope (bottom)
The adventure is accompanied by companions, and mica is particularly fond of running in parallel with quartz to form various types of metamorphic rocks. Complementary companionship may bring quartz shine again, as in the case of the recent explosion of "aventurine" (also known as aventurine jade), which is doped with chromium mica and other tiny minerals to give it its color and special optical effects (Figure 9). Conversely, "forced compromise" connections between companions can lead to rocks such as metamorphic mica, quartz, schist, etc., which are particularly susceptible to cracking (Figure 10).
Fig.9 Green aventurine is often used as a substitute for jadeite
Fig.10 Quartz-bearing schist prone to plate-like fractures
A happy reunion
"No matter how solid the rock is, it cannot withstand the repeated erosion of flowing water", and the rock composed of quartz will also be weathered and disintegrated under the action of natural forces such as flowing water and strong winds, and will be transported to distant places. However, in the process of migration, unstable minerals will be eliminated first, heavy minerals will settle first, and because quartz is one of the most stable minerals under surface conditions, the density is relatively small, so with the increase of the distance transported, the proportion of quartz in the material will continue to increase. Under the condition of flowing water transportation, the edges and corners of the minerals will be sharpened more and more round, and the particle size will become finer and finer. As a result, the lower reaches of many rivers have become sources of siliceous gems such as agate (which has the same chemical composition as quartz, but has a different structure) (Figure 11).
Fig.11 Agate
However, if the transported minerals are finally deposited in rivers/rivers/lakes/seabeds, they are compacted and reacted in a long geological time, and the rocks are formed again. Their legendary journey does not disappear in a vacuum, as the shape, size, and content of quartz have written biographies about this history. It is these rocks that sedimentologists study and test, read the rocks' travelogues and speculate on their geological journeys through the analysis of key information such as mineral relationships, composition, and age. Perhaps the two crystals that were once angular were washed away and shattered by the current, and finally reunited under the witness of the waves and currents to form a new rock (Fig. 12).
Fig.12 Hand specimens of quartz sandstone (top) and microscope (bottom),
90% of the grains in the picture are quartz>
Of course, the rock will also experience new disintegration, new torture and wandering. But the joy of the journey lies in the journey itself -
"I can't stay any longer.
Although the night is as hot as fire,
But if you stay any longer, you will solidify into rock.
How I wish I could take everything here,
And what can be done?
Just as an eagle cannot carry a nest,
I can only fly through the sun alone.
(Gibran, The Prophet)"
Isn't that the joy of geology?
Editor: Han Yatong
Proofreader: Liu Qijun Li Yuchao