Tuff rock or maybe not??

Source: Own photo, own work

Not far from the famous mural dedicated to the TV series "Derry Girls" we will find another intersting geological urban sculpture. It is a stone composition consisting of several different types of rocks. One particular rock stands out and deserves a closer attention. It is a type of rock which is clasified by geologist as an igneous rock, but it displays features which are typical to sedimentary rocks. 

The task of this Earthcache is to identify this type of rock at the ground zero and answers some questions related to it. 

Volcanic Rock

Source: Generated by AI

The rock we are dealing here with is of a volcanic origin and is classified as an extrusive igneous rock. It is not a very common rock that is used as building or sculpture material. It is in itself unique and cannot be found and observed so frequently as other mor common intrusive and extrusive igneous, sedimentary or metamorphic rocks.  Nevertheles, it has found its way to this ground zero location and has been used to create this interesting stone composition. 

I have already revealed part of the mystery that we are dealing with a special volcanic rock or another words extrusive ignous rock. I will provide below a description of two types of particular volcanic rocks. It will be your task to identify the correct type of the two types described below based on your observations and the given defnitions.

Tuff

Volcanic tuff is a type of a rock that is formed from volcanic ash, pumice, and other volcanic debris that has been explosively ejected from a volcano during an eruption. The material is then transported by air or water and deposited on the surrounding landscape, where it becomes compacted and cemented together to form a solid rock.
 Tuff is a type of volcanic rock with some features of sedimentary rock due to the fact that is composed of fine-grained volcanic ash and other volcanic debris. It is often porous and can be easily carved or sculpted, making it a popular building material throughout history.
Volcanic tuff can have a range of colors and textures depending on the type of volcanic material that makes up the deposits. It can be found in layers within volcanic ash deposits and is often associated with explosive volcanic activity. The thickness and extent of volcanic tuff deposits can provide important information about the magnitude and frequency of past volcanic eruptions. Material which forms vulcanic tuff is light and can travel greater distance, especially when carried by wind.

Volcanic Breccia

Volcanic breccia is an igneous rock. It is a type of rock that is formed from bigger than in case of tuff volcanic material, such as broken lava fragments, pumice, and ash, that are cemented together by a matrix of fine-grained volcanic material. Igneous rocks are formed from the solidification of molten rock material, and volcanic breccia is no exception. It is formed from volcanic material that has been ejected from a volcano during an eruption and then deposited on the surrounding landscape. Over time, this material becomes cemented together to form a solid rock. Material which forms volcanic breccie is heavier, consists of bigger debris chunks and can will not travel big distances. It is often found near volcanic vents.

Tasks/Questions:

At ground zero you will find a sculpture consisting of 7 blocks of rock. The picture (modified colors, so you really need to observe the rocks at ground zero) below shows numbers assigned to the individual blocks in the sculpture.  

Source: Own photo, own work

1. Block with which number is a extrusive vulcanic rock?
2. Which type of a volcanic rock is it, tuff or volcanic breccia?
3. Based on your observations and the information found in the listing, did the debris which formed this rock travel short or long distance from the volcanic vent? Explain shortly your answer.
4. What is the biggest volcanic debris fragment which you have identified in the rock?

Sources:

https://geoberuf.de/der-bdg/gestein-des-jahres/2011-tuff
https://www.britannica.com/science/tuff
Novi Asniar, Yusep Muslih Purwana, Niken Silmi Surjandari; Tuff as rock and soil: Review of the literature on tuff geotechnical, chemical and mineralogical properties around the world and in Indonesia. AIP Conf. Proc. 26 June 2019