China’s egg producing mountain: A geological mystery

In the hub of China’s Guizhou Province, there is a geological phenomenon that for years has kept locals and tourists quite puzzled. They refer to it as the “egg-laying mountain,” where at a cliff named Chan Da Ya, this mountain appears to “lay stone eggs” .
An unusual southeastern Chinese village has received media attention because of this mysterious cliff face that locals say, produces large, round rocks weighing as much as 660 pounds.These “stone eggs” are said to drop from the cliff once every thirty years, though scientists have yet to provide a definitive explanation for this occurrence.
In the village of Gulu Zhai, where the Shui people have lived for roughly a millennium, there is an egg-laying mountain-a weird natural wonder. The cliff itself is fairly small, only six meters wide and 20 meters in length. Not huge in size, perhaps, but an object of many imaginations nonetheless, as it supposedly lays stone eggs every thirty years. These are eggs that, once ejected, fall down to the ground, where they may lie waiting to be stumbled upon by a fortunate local.
This incident has been going on for hundreds of years, with stories passed down from generation to generation about an egg-laying mountain. Locals who have grown up hearing such tales often go on-site hoping to find one of these stone eggs. Eggs range in size from 20 to 60 centimeters in diameter, with some of the largest stones weighing more than 600 pounds. Dark blue in colour, and all but perfectly smooth, some cleaned and polished specimens can reflect sunlight well. Some eggs have weighed over 600 pounds.

Situated in the Sandu Shui Autonomous County, Gulu Village is the closest to this mystic Chan Da Ya cliff. An ancient region with a population of around 2,50,000 Shui people, the region covers more than 60 percent of the Shui population in China. The Shui, one of 56 ethnic minorities of China, have been living here since before the Han Dynasty. Despite the vastness of the region, Gulu Village itself was rather small, with a few dozen families living in it.
Since the discovery of the mountain laying eggs, over 100 stone eggs had been found at the foot of the cliff. Presently, about 70 of these remain in the village, every family possessing one or more depending on who found it. The rest are either sold or stolen. The Shui people esteem these stone eggs very high and believe they bring good fortune and luck. Indeed, they worship these stones. Almost every family owns a copy of them in the village. This is because they are seen to protect and bring good omen to their people, their animals, and their homes . Chan Da Ya Cliff is notable for its ancient inscriptions and carvings, which offer a glimpse into the historical and cultural context of the region. The site is significant for understanding the historical development of the area and its cultural heritage. Situated in Pingyao, Shanxi Province, the cliff is part of a broader historical landscape that includes the ancient city walls and various traditional buildings. Pingyao itself is a UNESCO World Heritage Site, recognized for its well-preserved example of a traditional Han Chinese city.

How such stone eggs came to be, still remains one of the most intriguing enigmas studied by today’s science. According to recent studies, the eggs, along with the host rock in which they occur, are of Cambrian Period age, dating about 500 million years. The Cambrian Period belongs to the Paleozoic Era and is famous for the so-called “Cambrian Explosion,” when the majority of Earth’s animal phyla first appeared and began to diversify significantly, manifested from the fossil record. Geologists speculate that this area was once under the sea and could also be one of the possible causes in forming these egg-shaped rocks over many thousands of years.

In the last 500 million years, because of the high temperature and pressure that these stone eggs were subjected to, they are now metamorphic rocks. Metamorphic rocks are any kind of pre-existing igneous or sedimentary rocks that have undergone substantial changes because of prolonged exposure to extremely high heat and pressure deep underground.
Professor Xu Ronghua of the Chinese Academy of Sciences’ Institute of Geology and Geophysics theorized that these stone eggs were made up of silicon dioxide, a chemical in ample supply during the Cambrian Period. He says that basically, the reason for the spherical shape of these stones is that a sphere has the smallest surface area compared with other shapes. In water, the silicon dioxide particles would naturally clump into spherical shapes, before these were subject to the forces which transformed them into metamorphic rocks.
The underwater environment was also conducive to the roundness and smoothness of the stones. As the rocks tumbled along the ocean floor in transport by currents and life forms, they would wear down into smoother, rounder shapes. Much like how sea glass is formed-or for that matter, how at-home rock tumblers will polish rocks-end.
The surrounding area of the cliff outside of the eggs, however, is different. The cliff itself is not made of metamorphic rock, the surrounding rock is made of calcareous rock, which is considered sedimentary rock. Sedimentary rocks can be found closer to the earth’s surface, and are made of compressed sediments such as sand, soil, or existing smaller rock pieces. Examples of sedimentary rocks include limestone, sandstone, and shale. With these sediments surrounding the stone eggs, it is possible they aided in compressing and separating them over the last 500 million years.

Do the stones get formed and fall off every 30 years?

Though it may appear that the stone eggs are being formed over the course of 30 years and being “birthed” by the cliffside, this is actually not the case. As it has also been mentioned earlier, it is believed that these stone eggs have been around for almost 500 million years. Through the course of time, the cliffside of the Chan Dan Ya has worn down due to weathering and erosion. In fact, eventual wear from changes in temperature and exposure to wind, water, ice, gravity, people, and animals can wear away at even the largest of rocks over time – including mountains.
This is because calcareous rock breaks down faster than metamorphic rock. Calcareous rock is primarily composed of calcium oxide, carbon dioxide and magnesium oxide.
They can also contain trace amounts of aluminum, iron, silicon, and water. The surrounding sedimentary calcareous rock breaks down faster due to its composition, revealing the stone eggs of a different composition over time. Because the metamorphic stone eggs aren’t breaking down with the surrounding cliff, they are falling out of the side as it wears away.
People from Gulu have estimated that each of the stone eggs take some 30 years to be “laid” by the mountain from their appearance on the cliff to their falling to the ground. An egg just beginning to make its appearance might be 30 years away from falling, while one already partway out could take another 10 or 20 years to go. Since each stone egg was at a different position within the cliff, with a little theory, one would be bound to fall at any point for the next person who found one.
As the mountain further erodes, stone eggs could start to appear along paths that are regularly followed by local Shui and tourists touring the region to reach it. If this happens, travel for both people and pack animals could be much more difficult and arrangements would probably have to be made to have the visible eggs removed by hand or ground smooth.

Dying mountain?

With time, the mountainsides will wear down, and more stone eggs will surface on the cliff and fall to the ground. Also, the eggs may start to emerge at the tops of the mountain as it erodes by foot activity. Geologists are not sure exactly how many eggs remain in the mountain, but theoretically, they could be throughout the entire mountain if the region contained enough silicon dioxide during the Cambrian Period. Ultimately, nobody will know until the mountain runs out of stone eggs-if it ever does.
Over the next several thousand years, the mountain will continue to erode into the soil, leaving these eggs behind. If the eggs are not being collected any longer, they will be on the ground where they, too, will break down and form sediments which later on will form the building of new sedimentary rocks. Such is the rock cycle we all learned in grade school. If humans continue with this careful collection, the stone eggs can be preserved for far longer without exposure to the factors of weathering like soil, wind, water, and ice.

Do other such mountains exist?

Although Mt. Gandang has been the first location identified to have these stone eggs, other locations may be found to occur in unexplored mountainous regions. It is also possible that future mountains would have more of these stone eggs. Currently our oceans contains 30 ppb or parts per billion of silicon dioxide, and the earth’s crust is made of 59% silicon dioxide.
Considering the huge amounts of silicon still present in the earth and in the oceans, it is fairly possible that new-made eggs may be found in future mountains several million years from now. Though we personally won’t be around to see these egg-laying mountains laying their eggs, perhaps those who will see it will be just as fascinated by it as we are.