Almandine

The intention with this earthcache is to be able to recognize the mineral almandine, a gemstone-like material that appears as "spots" in rocks and in rock mass. The fascinating thing about Almandine is that it can tell us about how the bedrock has been formed, about how the rocks have been developed in different eras, how deep they have migrated in the earth's crust, how the temperatures in the earth's crust have varied and how quickly mountain ranges have changed . In other words, it can teach us about the conditions deep down in the mantle at research level. The information can be read out from chemical changes in the crystal, from the grain boundaries against surrounding minerals, and from structures and small inclusions of other minerals that have been encapsulated in the garnet during its journey. 

At the location, you will witness a rock sprinkled with Almandine. Almandine is referred to as a precious stone and used in jewellery, among other things. The mineral is special because it preserves information about its journey through the Earth's crust as it grows. So Almandine is well liked among scientists and geologists. Here you will get to study the wonderful colours based on the minerals that appear close to each other, some dominant while others somewhat less visible and decorative. The colour of the mineral reveals the decoration immediately, while you will also see a different play of colours from the rock that the Almandine is surrounded in. If you bring a lantern, you will be better able to study its shine and shine, as well as get a better detailed overview of the crystal deposit. Focus on the red mineral to be able to answer the questions.

The mineral:

What is a Garnet? Garnet is the name used for a large group of rock-forming minerals. These minerals share a common crystal structure and a generalized chemical composition of X₃Y₂(SiO₄)₃.

Most garnet forms when a sedimentary rock with high aluminium content, such as shale, is metamorphosed (subjected to heat and pressure). The high heat and pressure breaks the chemical bonds in the rocks and cause minerals to recrystallise.

This is a mineral group that has been used for a long time and is especially well known because it has been used in its form as gemstones and abrasives, especially in the Bronze Age. Garnets have strong, beautiful colors and have a high luster. It can be cut and is used as a gemstone. Garnet is also used as an abrasive due to its enormous hardness with a mineralogy of 6½–7½.

The mineral crystals are usually deep red or brown, almost black or light yellow to green. In other words, a wide range of colours. The mineral must not be confused with amber, this can be explained by the fact that the group of mineral is much harder and has a more crystalline surface.

Garnet crystals are usually deep red or brown, almost black or light yellow to green. In other words, a wide range of colours. The Almadines deep  red colour originates from the iron oxide content that is to be found in the mineral. Garnets must not be confused with amber, this can be explained by the fact that garnet is much harder and has a more crystalline surface.

Garnets most often occur in a dodecahedral crystal structure (a polyhedron with twelve side faces). Garnets crystallize in a cubic system, ie with three axes of equal length and all perpendicular to each other. Grenades have no cleavage angle.

Structure and occurrence:

The occurrence is actually a whole group of silicate minerals with the same crystal structure, where individual silicate tetrahedra form connections with a wide range of cations, such as magnesium (Mg2+), iron (Fe2+), manganese (Mn2+,), calcium (Ca2+), aluminum (AI3+) and chromium (Cr3+). Depending on the chemistry, garnet appears in many different colours. The most common garnet, ferruginous almandine (Fe3AI2(SiO4)3), is dark red while calcium-bearing garnet, grossular (Ca3AI2(SiO4)3), is green to dark green in colour.

Garnet occurs mainly in metamorphic rocks. Based on the knowledge of garnet's melting point curve in relation to pressure, it is used to determine the pressure and temperature level under which the rock was formed. Garnet occurs most frequently in metamorphic rocks such as marble, mica schist, gneiss and amphibolite.

Characteristics:

Almandine often occurs in metamorphic rocks (transformation rocks) such as mica schists, amphibolites and gneisses. The mineral can also occur in pegmatites and contact metamorphic rocks. Almandine is a garnet in the pyralspitt series and forms sacrificial chemical series with the garnets spessartine and pyrope.

*  The crystals are deep red or brown, almost black or light yellow to green. Gem-like luster, glass luster.

*  Garnet is a very hard mineral and falls under the Mohs hardness scale as no. 7

The Mohs scale  is a relative and somewhat random scale of scratch resistance, and the difference between the various levels can vary greatly in relation to absolute hardness. Absolute hardness, on the other hand, is determined during controlled laboratory tests, but this scale is only used to a small extent. 

Mohs hardness 7 ,  Absolute hardness 100 ,  in the class with Quartz – SiO ₂

*  Dodecahedral crystal structure, Characteristic cubic crystals

*  Density 3.5-4.3 g/cm3

To log this cache.

To get to log this cache you will have to visit and answer the questions which are related to the coordinates given the earthcache.

When answers are collected, send them to CO for verification.

You can log immediately after answers are sent CO. If there are any questions about your answers CO will contact you.

Logs without answers to CO or with pending questions from CO will be deleted without any further notice.

Please do not include pictures in your log that may answer the questions.

Questions:

1.  Answer the questions under by visiting the coordinates.

A.  Go to the given location and carefully study the almandines you find here at GZ. How big in mm size are the biggest mineral you can observe? And is the mineral only found in certain places in the rock, or all over the place? 

B.  Which of the given colours image (example)  : A, B, C and or D is similar to what we find here at the location? 

C.  Can you say something about whether the Almandine here contains iron or calcium?

2.  Take a picture of you, you or your GPS and attach it to the log. Without revealing any of the answers!