历史背景
从天坛南门到祈年殿，有一条轴线连接了天坛中的祭坛。这条轴线划分为了三条小道。中间的汉白玉石板大道为“神路”，意思是给天神降临后行走用的；东侧的砖砌路为“御路”，是专门给皇帝用的；而西侧的“王路”则是留给王公大臣的道路。只是在祭天的路上，都有如此严苛的规定，就算是位极人臣的君王，也不敢踏足中间的“神路”，只能在“御路”上行走前进。丹陛桥还有着独特的北高南低设计，向北行走时，会步步登高，如登天界。
地质现象的位置
神道位于天坛公园内，GZ位于丹陛桥上，开放时间是8:00至17:00。如果您错过了开放时间，可以参考waypoints去观察神道的其他部分。
汉白玉
汉白玉是一种白色的细粒大理岩，为石灰岩变质而来的岩石，内含闪光晶体。汉白玉的主要成分是碳酸钙，次要成分MgCO3和SiO2，也包含少量Al2O3、Fe2O3等。汉白玉质坚硬，是上等的建筑和雕刻材料，从中国汉代起，就用这种石料制作宫殿中的石阶和护栏。汉白玉的产量约占所有大理石产量的30%。
变质作用
变质作用是指现有岩石（原岩）转变为具有不同矿物成分或结构的岩石的过程。变质作用发生在超过 150°C (300°F) 的温度下，通常也伴随着高压或化学活性流体的存在，但岩石在转变过程中基本保持固态。变质作用不同于风化作用或成岩作用，后两者是指发生在地球表面或地表以下的变化。
变质作用有多种形式，包括区域变质作用、接触变质作用、热液变质作用、冲击变质作用和动力变质作用。这些变质作用的特征温度、压力、发生速率以及反应性流体的参与程度各不相同。在压力和温度不断升高的条件下发生的变质作用称为顺行变质作用，而温度和压力不断降低的条件下发生的变质作用称为逆行变质作用。
变质岩石学是研究变质作用的学科。变质岩石学家主要依靠统计力学和实验岩石学来理解变质过程。
风化作用
风化作用为岩石、土壤以及矿物等与地球大气层接触而分解。侵蚀作用包括岩石和矿物经由媒介如水、冰及重力等引起其瓦解。侵蚀作用常伴随着搬运作用，要注意两者并非相同，风化作用着重于由内而外去崩解，侵蚀作用则是由外而内去剥落。
风化作用可以分为物理性与化学性。
物理风化，也称机械风化或崩解，是指岩石在不发生化学变化的情况下发生崩解的一系列过程。物理风化是指岩石通过膨胀和收缩等过程（主要由温度变化引起）破碎成更小的碎片。两种常见的物理崩解类型是冻融风化和热裂解。压力释放也会导致岩石在不发生温度变化的情况下发生风化。物理风化通常远不如化学风化重要，但在亚北极或高山环境中可能较为显著。此外，化学风化和物理风化往往同时发生。例如，物理风化扩展的裂缝会增加岩石暴露于化学作用的表面积，从而加速崩解。霜冻风化是物理风化最重要的形式。其次是植物根系的楔入作用，植物根系有时会进入岩石裂缝并将其撬开。蠕虫或其他动物的掘穴活动以及地衣的“拔蚀”作用也有助于岩石的崩解。
化学风化是指水、氧气、二氧化碳和其他化学物质与岩石发生反应，改变其成分的过程。这些反应会将岩石中一些原生矿物转化为次生矿物，去除其他物质作为溶质，并留下化学性质不变的稳定矿物。实际上，化学风化将岩石中原有的矿物组成转变为与地表环境更接近平衡状态的新矿物组成。真正的平衡状态很少能达到，因为风化是一个缓慢的过程，而且在风化反应产生的溶质积累到平衡水平之前，淋滤作用就会将其带走。这种情况在热带环境中尤为明显。水是化学风化的主要作用力，它通过统称为水解的反应，将许多原生矿物转化为粘土矿物或水合氧化物。氧气也十分重要，它能氧化许多矿物，二氧化碳也是如此，它们的风化反应被称为碳酸化作用。
您的任务
请通过消息中心或电子邮件将以下问题的答案发送给我。然后，您可以立即记录Earthcache。如果您在回答问题时遇到任何问题，请随时与我联系 - 我很乐意为您提供帮助。如果Log后七日内我没有收到您的消息或邮件，或您在Log中直接回答了问题，我将删除您的Log。
1️⃣ 请您估测一下石板的长度与宽度。
2️⃣ 请您观察神道石板的颜色，并触摸石板表面，它是光滑、粗糙还是有轻微凹坑？这说明石板经历了怎样的作用？
3️⃣ 您在石板上观察到了哪些纹理？请描述并分析其纹理的成因。
4️⃣ 请在神道上拍摄您自己、GPS 或属于您的其他物品的照片，并将其附加到您的日志中。
Historical Background
From the South Gate of the Temple of Heaven to the Hall of Prayer for Good Harvests runs a central axis that connects the major sacrificial structures. Along this axis are three parallel pathways, each with a distinct ritual function.
The central alabaster avenue is the Divine Path (Shen Dao), believed to be the route taken by heavenly deities when descending to the altar. To its east lies a brick-paved Imperial Path, reserved exclusively for the emperor. To the west is the Path of Nobles, used by princes and high-ranking officials. Even on the road to the most sacred of ceremonies, such strict rules applied that no minister or noble, regardless of rank, dared to step onto the Divine Path; they could only walk along the Imperial Path. The Danbi Bridge is built with a unique higher-north-lower-south slope, creating the sensation of ascending toward the realm of heaven as one walks northward.
Location of the Geological Phenomenon
The Divine Path is located inside the Temple of Heaven Park. The GZ is on the Danbi Bridge, which is open from 08:00 to 17:00.
If you arrive outside of opening hours, you may use the listed waypoints to observe other accessible sections of the Divine Path.
Hanbaiyu
Hanbaiyu is a fine-grained white marble formed through the metamorphism of highly pure limestone, containing tiny sparkling crystals. Its primary component is CaCO₃ with minor amounts of MgCO₃ and SiO₂, as well as trace oxides such as Al₂O₃ and Fe₂O₃.
Dense and durable, it has long been regarded as an excellent material for construction and sculpture. Since the Han dynasty, hànbáiyù has been widely used in palace architecture, especially for steps, balustrades, and ceremonial structures. Today, it accounts for about 30% of all marble production in China.
Metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface.
Various forms of metamorphism exist, including regional, contact, hydrothermal, shock, and dynamic metamorphism. These differ in the characteristic temperatures, pressures, and rate at which they take place and in the extent to which reactive fluids are involved. Metamorphism occurring at increasing pressure and temperature conditions is known as prograde metamorphism, while decreasing temperature and pressure characterize retrograde metamorphism.
Metamorphic petrology is the study of metamorphism. Metamorphic petrologists rely heavily on statistical mechanics and experimental petrology to understand metamorphic processes.
Weathering
Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs in situ (on-site, with little or no movement), and so is distinct from erosion, which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity. Weathering processes are either physical or chemical. Physical weathering, also called Mechanical weathering or disaggregation, is the class of processes that causes the disintegration of rocks without chemical change. Physical weathering involves the breakdown of rocks into smaller fragments through processes such as expansion and contraction, mainly due to temperature changes. Two types of physical breakdown are freeze-thaw weathering and thermal fracturing. Pressure release can also cause weathering without temperature change. It is usually much less important than chemical weathering, but can be significant in subarctic or alpine environments. Furthermore, chemical and physical weathering often go hand in hand. For example, cracks extended by physical weathering will increase the surface area exposed to chemical action, thus amplifying the rate of disintegration. Frost weathering is the most important form of physical weathering. Next in importance is wedging by plant roots, which sometimes enter cracks in rocks and pry them apart. The burrowing of worms or other animals may also help disintegrate rock, as can "plucking" by lichens. Chemical weathering takes place when water, oxygen, carbon dioxide, and other chemical substances react with rock to change its composition. These reactions convert some of the original primary minerals in the rock to secondary minerals, remove other substances as solutes, and leave the most stable minerals as a chemically unchanged resistate. In effect, chemical weathering changes the original set of minerals in the rock into a new set of minerals that is in closer equilibrium with surface conditions. True equilibrium is rarely reached, because weathering is a slow process, and leaching carries away solutes produced by weathering reactions before they can accumulate to equilibrium levels. This is particularly true in tropical environments. Water is the principal agent of chemical weathering, converting many primary minerals to clay minerals or hydrated oxides via reactions collectively described as hydrolysis. Oxygen is also important, acting to oxidize many minerals, as is carbon dioxide, whose weathering reactions are described as carbonation.
Your Tasks
Please send your answers to the following questions via Message Center or email. After submitting your answers, you may immediately log the EarthCache. If I do not receive your answers or message within seven days after your log, or if you post the answers directly in your log, your log will be deleted.
1️⃣ Please estimate the length and width of the stone slabs.
2️⃣ Observe the color of the slabs, and touch the surface. Is it smooth, rough, or slightly pitted? What does this tell you about the processes the stone has undergone?
3️⃣ What kinds of patterns or textures can you see on the slabs? Please describe them and explain what might have caused these features.
4️⃣ On the Divine Path, please take a photo of yourself, your GPS device, or another personal item, and attach it to your log.