Elephant of Lentas - Rock hardness

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The geology of Crete is diverse and offers many impressions of the earth's history. In this Earthcache we would like to explain to you the different hardnesses of rock-typs.

IMPORTANT ! You absolutely need a knife, without you can NOT solve the EC!

Please also note that you should not do the EC in stormy seas! Do not risk your life or your healthy!

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Rock-types

In the geosciences, rocks are divided into magmatic, metamorphic and sedimentary rocks according to their origin, and into loose and hard rock according to their degree of consolidation. Stonemasons are familiar with these distinctions, but they are of secondary importance in technical processing. They also distinguish between soft- and hard rock when they work on it. In practical application for consumers in the construction industry, this means, for example, that hard stone cannot be scratched with a kitchen knife or scratched in normal use. The division into soft or hard stone follows the logic of the use of tools and is a sensible classification of how stone is processed manually, sawn by machine or ground.

With the different formations, it can always come to a mixture of different rocks or rock layers. This often results in different properties in a small space. Coastal erosion or (geological) abrasion can be seen here on the beach, for example, as the gradually progressive change in (sea) coasts due to erosion by tides, waves and weather influences such as wind, rain and temperature differences, natural events such as hurricanes or earthquakes, but also through impacts on the environment, such as damage to the top soil layers through human influence or global warming. Of course, the different hardness of the rock plays an important role.

Here some examples (not all on Crete):

soft rock:

marbles, Limestone and dolomite, travertine, tufa and so-called onyx marble, Alabaster, sandstones, Vulcanites (except rhyolites, lamprophyres, hard tuffs as ignimbrites and basalts, which are hard rocks), Serpentinites, clay slate

hard rock:

gabbros, Norite, Tonalite, granites, granodiorites, diorites, syenite, monzonite, Aplite, Pegmatites, lamprophyres, anorthosites, Larvikite, Gneiss, migmatite (gneiss), Paragneiss (gneiss), Orthogneiss (gneiss), granulite (gneiss), mica schist, basalts, quartzite, foil syenite, rhyolites, diabase, picrite

On Crete, all geological levels of the South Aegean island bridge are exposed. The limestones on Crete can mainly be seen in the last elevations of the island. Plated marbles with layers of chert usually dominate here, which transition into a flysch in the east of Crete. Characteristic of the following phyllite-quartzite series of East Crete are Variscan bedrock chips. The massive limestones and dolomites border on the phyllite-quartzite series or directly overlie the autochthonous rocks; for example in the Psiloritis massif. In the Upper Triassic the deposition of carbonate rocks of the Tripolitza series begins. They show steep rises and pronounced karst forms. In the Middle to Upper Eocene they are replaced by a marly flysch. The rocks of the Pindos series are represented in small nappe remains or floes. It is characterized by an alternation of platy, chert-bearing limestone with marls and clay rocks and light-colored, platy limestone with only a few cherts. Almost all of the ophiolite deposits can be found in central Crete. In the central south, where you are now, you will mainly find gneiss. This is bordered by flysch (alternation of mudstones and coarser-grained rocks -- typically sandstones) and softer sedimentary rocks.

How can you now determine on site whether you have hard rock or soft rock in front of you? You can do that relatively easily with a knife, which you absolutely need. So go to the beach (waypoint), carry out the experiments, take the corresponding pictures and send them to us together with the answers. Unfortunately, we have to delete logs without corresponding pictures and answers without comment. If something is wrong with the answers, we will contact you.

Tasks:

1. Name a few hard rocks that occur on Crete.
2. Name a few soft rock that occur on Crete.
3. Which type of rock is mainly found in this area?
4. On the beach: look for different stones lying around and try to carve them with the knife. Documented the attempt in the picture. Describes whether you have a hard- or soft rock. Describe the appearance and texture of the rock in your own words.
5. On the beach/larger pile of rocks: look at the pile of rocks and try the knife here as well. Which rock is it? Describe the surface and appearance in your own words.
6. The Lentas Elephant: swim to the elephant and examine the rocks there. Also describes the texture, appearance and hardness.
7. In your opinion, what rock is the elephant made of ?
8. How could the Elephant arise in relation to different types of rock?
9. Take a picture of yourself on the beach with the elephant in the background. You can send us the picture or attach it to the log as you like.

We wish you a lot of fun on THE island of Crete, your KalimeraM and Patchwork Rudel 😊

Sources: own observations, Wiki