Welcome to my Earthcache! An Earthcache is a special type of geocache where there is no container to find – instead you are looking for a unique geological feature of the area and need to answer questions, as well as posting a picture, in order to claim the find. The goal of this Earthcache is to explore marble as a metamorphic rock, how it forms, why it deforms, and why marble rarely exists in a perfectly “pure” state. You will also learn how minerals, impurities, and geological processes create the beautiful colours, banding, and inclusions visible in many monuments. All observations can be made from the posted coordinates without disturbing any graves or markers within Crown Cemetery. This cemetery can be accessed by the public from 8:00am until dusk, seven days per week. 

At the posted coordinates, you are looking for two square marble monuments - one for the FARNHER family, and one for GEORGE ELFNER. Theye stones are within about 6m of each other - there should be no need to wander around looking for them. They are in the same row. 

EARTHCACHE REQUIREMENTS

As with all of my ECs, I am not looking for PhD-level responses, but I am hoping that you take some time to enjoy the area and learn something new. Please include a list of all cachers with your answer if logging as a group, noting that each cacher must upload their own photo.

To claim a find for this EarthCache, send your answers to the questions below using the Message Center or the link at the top of the cache page. You may log your find immediately as long as your required photo is included. I will contact you if there is a problem with your answers.

Observational Task

At GZ you will find marble monuments displaying a range of colours, textures, veins, and patterns. Some are smooth and lightly banded, while others show dramatic folding, fracturing, or deformation. Look closely at how the minerals within each stone behave. You may also notice small dark flecks, streaks, or irregular patches — these are inclusions, which tell an important story about how the marble formed deep within the Earth.

1. Texture and Deformation: Describe the surface of the marble. Is it smooth, veined, folded, or fractured? What signs of deformation do you observe, and which monument shows the greatest amount of structural change?

2. Colour and Banding: List the colours you observe. Are they arranged in streaks, bands, swirls, or zones? Based on the geology lesson, what minerals or impurities may be responsible for these colours?

3. Inclusions: Do you see any dark flecks, spots, streaks, or irregular patches that are different from the rest of the marble? Describe what they look like. Based on the geology lesson, what might these inclusions represent?

4. Metamorphic Grade: Based on its texture and deformation, do you think this marble formed under high or moderate metamorphic conditions? Explain your reasoning.

5. Photo: Mandatory. Include a photograph of yourself, your GPS, a signature item, or thumbs up at the monument. You do not need to show your face, but the photo must be unique to you. Each cacher must upload their own photo.

Earth Science Lesson

How Marble Forms and Recrystallizes

Marble begins as limestone or dolostone deposited in warm, shallow seas where carbonate muds and shell fragments accumulate. Over long periods of burial, these carbonates become exposed to elevated temperatures and pressures during tectonic events such as mountain building or contact with intruding magma. Marble typically forms between 600°C and 800°C, at depths ranging from 15 to 30 kilometres.

Under these conditions, the tiny calcite or dolomite grains that originally made up limestone begin to recrystallize into larger, interlocking crystals. All original features—fossils, bedding planes, pore spaces—are gradually erased. As recrystallization continues, the rock becomes denser, more crystalline, and capable of taking a smooth polish. This is the marble used in monuments today.

Deformation: How Marble Bends, Folds, and Flows

While marble is brittle at the surface, deep underground it behaves plastically, flowing or bending rather than breaking when subjected to tectonic pressures. Compressional forces can fold marble into sweeping curves or tight convolutions. Shear forces may stretch and smear minerals, producing ribbon-like patterns. Mineral-rich fluids moving through the rock can create veins which may later be folded or offset during additional deformation.

The degree of deformation in a marble depends on how strongly, how long, and from what direction tectonic forces were applied. Some marbles record intense mountain-building events, while others experience only mild metamorphism and remain relatively uniform.

Inclusions in Marble: Why Marble Is Rarely “Pure”

Although marble is often imagined as a flawless white stone, true pure marble is extremely rare. Most marbles contain inclusions — pieces of other minerals or rock fragments that became incorporated during recrystallization. These inclusions can appear as dark specks, streaks, nodules, or irregular patches.

Common types of inclusions include:

• Graphite or carbonaceous material from organic-rich layers in the original limestone

• Clay, mica, or quartz grains trapped within the carbonate before metamorphism

• Iron-rich minerals such as hematite or goethite, which create reddish or brown spots

• Siliceous chert fragments from impurities in the original sediment

• Recrystallized fluid-deposited minerals such as pyrite or quartz

During metamorphism, these materials cannot dissolve into the calcite matrix, so they become stretched, smeared, or concentrated into bands. Many inclusions record their own small-scale histories of deformation, providing valuable clues about the conditions under which the marble formed.

Why Colours in Marble Matter

The colours in marble are not random. Each hue represents a specific mineral or impurity:

• White: nearly pure calcite or dolomite

• Grey or black: graphite or finely disseminated organic carbon

• Pink or red: iron oxides (hematite), iron-rich clays, or weathered pyrite

• Brown or yellow: limonite, goethite, or other hydrated iron minerals

• Green: serpentine, chlorite, or other magnesium-rich silicates

• Blue-grey: carbonaceous material mixed with fine-grained mica

• Cream or tan: clay minerals, mica, or dolomitic impurities

These colours often appear in bands or streaks because differential pressure during metamorphism causes impurities to migrate and segregate into layers. Each band records the rock’s chemical composition, the direction of tectonic forces, and the intensity of metamorphic processes.

Weathering and Erosion in Marble

Although marble is durable, it is highly reactive with weak acids. Rainwater absorbs carbon dioxide from the atmosphere, forming carbonic acid, which slowly dissolves calcite. As a result, softer zones (often purer calcite) weather more quickly than harder layers containing quartz, mica, or iron-rich minerals. This selective weathering creates the grooved, recessed, or textured surfaces commonly seen on old marble monuments.

Important Visitor Information

The cemetery is closed from dusk until 8:00 a.m. Do not attempt this EarthCache outside of these hours.
Please behave respectfully, as this is an active burial site. Keep noise low, do not disturb memorials, and follow all posted rules.

AI Content Disclosure
Some of the descriptive text and/or images on this page were created with the assistance of artificial intelligence tools. All information has been reviewed, verified, and edited by the cache owner for accuracy and clarity.

This cache was placed by a PROUD Platinum Earthcache Master.