Breakfast.Cheese.Apple EarthCache

Introduction

I know what you're thinking - Breakfast.Cheese.Apple - that's an unusual name for an EarthCache! 😯

And yes, it does look a bit weird, but there is a point to it 😉.

You might even be thinking that the name represents the coordinates of the location in what3words format but I can assure you it's not as, while that arrangement of three words is linked to a geographical location, it's somewhere in Norway, which definitely isn't the EarthCache location.

The subject of this EarthCache is breccia, which is one of those words I look at and immediately mispronounce . So I thought a good place to start would be with a guide to pronunciation - but I've never been able to fathom those weird pronunciation guides in dictionaries and the like. According to a dictionary source the word breccia is pronounced like this - /ˈbrɛtʃə//ˈbrɛtʃɪə/ - deciphering of which, to me at least, requires several references to a table .

So here's my simple guide - take bre from breakfast, ch from cheese and a from apple and put them together and that's how you pronounce breccia .

That's how the first set of dictionary scribbles are suggesting breccia should be pronounced anyway. For the second set put together bre from breakfast, chee from cheese and a from apple

Wonder if I could get a job as a lexicographer? 🤔

So, now you know how to pronounce breccia - what on earth is it?

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Based on your study of the area of breccia at the cache location and using the information on the cache page please tell me:

1. The breccia is spread at ground level over an area of several square metres. Take a good look at it and describe its appearance in some detail - then tell me which of the three classifications on the cache page is the best fit for this particular breccia.
   
   
2. To identify any minerals between the breccia clasts you'll need to see associated colours - which is easily possible if you look closely enough BUT not only will it be a whole lot easier if the rock is wet, you'll get to see how dramatic this breccia really is. The special tool you'll need is WATER - a couple of litres should do. If you're lucky the tide will have left some pools you can use to re-fill your bottle. What mineral or minerals are evident between the breccia clasts?
   
   
3. What is the approximate RANGE of clast size in this breccia, from smallest to largest?
   
   
4. Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
   
   

Breccia - what on earth is it?

Well, I used to think this was a simple question with a simple answer but the more I studied the more confused I became because there seemed to be lots of online definitions which were contradictory or inaccurate 😵.

It turns out there are more types of breccia and more ways to describe and classify it than I first thought - but I wanted to start off here with a definition that was technically accurate while being general enough to apply to the full breccia spectrum - so here it is:

Breccia is rock composed of angular fragments of older rocks, stuck together.

A few other general truths about breccia are:

• The angular rock fragments are also known as clasts
  
  
• The source of the clasts may be one single type of rock (monomictic) or a combination of several different types of rock (polymictic)
  
  
• Sometimes it's easy to see how some individual clasts used to fit together with others to form a larger whole, and sometimes it isn't
  
  
• The clasts may be sharply angular but they may also have undergone some rounding as a result of abrasion (grinding against other clasts) or parts of them being dissolved
  
  
• The degree of sharpness / roundness may vary to some degree from clast to clast
  
  
• The spaces between the clasts are filled with finer material called matrix and/or mineral cement
  
  
• The clasts and matrix may be of the same type of rock or each may be of a different type of rock
  
  
• The ratio of clasts to matrix can vary quite a lot - breccia can be mostly clasts with a small amount of matrix or mostly matrix with a small quantity of clasts - and everything in between
  
  

What does it look like and how does it get that way?

The short answer to the first part of that question is that it looks like angular fragments of rock surrounded by finer material called matrix, and/or mineral cement.

Because there are numerous different types of breccia formed in numerous different ways, the answer to the second part of the question could easily extend to reams of information way beyond what you need to know in order to complete this EarthCache.

A few basics are all that's really required here and to that end I offer, as a guide, the following table:

So - to explain the table...

The table is divided into two rows and three columns with five example images per row, straddling the three columns. The images in the table offer a guide to what breccia might look like as a result of variation in two of its properties - clast concentration and clast rotation

Variations in these two properties dictate which of three classifications is used to describe a particular breccia - whether it's a crackle breccia, a mosaic breccia or a chaotic breccia (also known as a rubble breccia)*.

In the first row the only property which changes is clast density i.e. how tightly packed the clasts are / how much space between the clasts is filled with matrix and/or mineral cement.

The first image shows 100% clast concentration - the clasts are all bunched up tightly together with no space between them. At this stage the breccia is essentially almost solid rock and would be classed as a crackle breccia.

At 75% clast concentration (i.e. 25% matrix/cement) we start to transition from the realms of crackle breccia into mosaic breccia.

Around 60% clast concentration (40% matrix/cement) we transition into a third type of breccia - the chaotic or rubble breccia.

And there's more 😉...

In the second row, in addition to variations in clast density we see varying degrees of clast rotation and examples of how these two parameters together can affect the way a breccia looks.

One key thing to notice is how much more difficult it is to see which clasts had previously fit together with others to form a larger whole. This becomes even more difficult or perhaps impossible if the clasts have also been rounded due to abrasion or parts of them being dissolved.

*There are lots of other types of breccia, some with cool names like micro-breccia, mega-breccia and even pudding breccia, so called because it's mostly matrix and cement and the few clasts scattered throught it are vaguely reminiscent of raisins in a pudding

In summary then - the rules of this particular method of classifying breccia (there are other methods):

• Crackle breccia: A breccia consisting of at least 75% clasts over 2 mm in diameter. The clasts have undergone less than 10° of rotation.
  
  
• Mosaic breccia: A breccia consisting of 60-75% clasts over 2 mm in diameter. The clasts have undergone 10-20° of rotation.
  
  
• Chaotic breccia: A breccia consisting of 30-60% clasts over 2 mm in diameter. The clasts have undergone over 20° of rotation.
  
  

Mineral traps

Now we might look at breccia and think that it's just rock that's been smashed up, sometimes mixed up (if the source material comes from more than one rock type), and then stuck back together again - and that's largely true.

Breccia though is of particular interest to people looking for sources of valuable minerals - because spaces between the clasts or any matrix material can be filled with water, rich in minerals which, over time, crystallise into solid mineral deposits which can later be mined or quarried.

Different minerals have different colours which can help to identify them - but the colours are not unique to individual minerals and so identification by colour alone isn't 100% reliable.

For the purposes of this EarthCache though colour will suffice for identification of any minerals which might be found in this particular breccia and, to that end, you'll see that in the table to the right I've listed just one mineral per colour.

If you've carefully read and digested the information from this cache page your tasks at the cache location should prove relatively straight forward, although you may wish to take a printed copy of the page with you so that you can check your answers while there .

Please submit your logging task responses before posting your log.