SAND WORKSHOP Showing the different materials: Do you know this material? Do you know its name? Sand, of course. Is this one sand as well? Yes, it is fine sand. Is this other one sand as well? Yes, it is coarse sand. And this one? Of course not. It’s smaller. We can call it mud. Please, don’t sneeze! And this one? Of course not. It’s bigger. We can call it gravel. Have you seen it before? Where? Fine gravel, coarse gravel... And cobbles. And blocks. What’s the sand size? The sand is smaller than 2 millimetres and bigger than 0,06 millimetres. Can we measure it? How can we do it? What do we need? A magnifying glass and a rule. Clay / Mud (Argila): <0,0039 mm Silt / Mud (Llim): 0,0030-0,0625 mm Sand (Sorra): 0,0625-2 mm (coarse sand, medium sand 0,25-0,5 mm, fine sand) Gravel / Pebble (Grava): 2-64 mm Cobble (Còdol): 64-256 mm Boulder / Block (Bloc): >256 mm Which size is the Empúries sand? Before going to check... Look at this bottle. Let’s put a little amount of coarse, medium and fine gravel, another little amount of coarse, medium and fine sand, and finally another amount of mud. And now fill up the bottle of water, mix the content and... let the bottle rest. Where’s the gravel now? In the bottom of the bottle. Where’s the sand? On the gravel but it has crept through the holes. Where’s the mud? It is mixed with the water... Suspended. Let’s the experiment rest a little more. And we’ll go to the beach for a while. The size of the Empúries sand is between... and... One grain! Another grain! Millions of grains! Are all the grains exactly the same? Which differences can you notice? The colours, of course. Which colours have you detected? Brown, yellow, red, orange, grey, white, black... And transluced... Not transparent. Are there... many / quite a lot / a few / none? Which is the predominant colour? What does it mean? Perhaps this means that each grain is made of a different mineral. Let’s do an experiment! Do you know what hydrochloric acid can do? If the material is granitic or volcanic... the hydrochloric acid does nothing at all. But if the material is calcareous... the hydrochloric acid does bubbles. Why? Because the hydrochloric acid detects lime. For example, the lime of the shells.

What about the Empúries sand composition? It is made of... shells? calcareous rock? different types of materials? Who may have mixed (carried on, transported, brought) all these materials? Let’s have a look to the map. The old Ter river? The Fluvià river? The Muga river? The Mediterranean sea? The Cap de Creus rocks? The Montgrí rocks? The Tramuntana wind? All of them? We must accept that the rivers work is basic. Let’s have a look around the Rec’s beach. Are there any different materials than sand? Mud and gravel. How is the gravel like? Round (rolling stones). Why? Because of fluvial transport. Gravel and mud are compacted. Why. Because water has dried. We call it just soil. Is sand compacted when the water is dried? Never. Because of this, sand and the other materials are never compacted altogether. Finally, let’s return to the classroom and talk about the utilities of the sand. Do you know if we use the sand someway? How? Playing in the beach. Playing in the schoolyard. Making sculptures. Making sand castles… Is there sand in your house? Where? Into the walls, of course! The sand is an important component of the mortar (or concrete) used in the construction of the buildings. Shore sand o fluvial sand? The bricklayers only use fluvial sand. Why? Because of the salt! The salt doesn’t fit cement. And in the roman city? They didn’t know cement, but they used lime. Lime in Catalan is... calç. Look at this mortar wall. It is more than twenty centuries old. But, do you remember the water tanks? They filled them with rainwater. And the rainwater had to be cleaned before entering the tanks. How did they do? With filters. Sand filters. Like this one. Does it work? Let’s have a look to the sediment bottle. Can we remark any difference from before? Yes, the mud has sedimented a little bit. Let’s mix again, to obtain very dirty water. What will happen if the pour the dirty water into the sand filter? Let me remark that this filter is small and simple. Look at this photograph! So, is the beach sand doing some work with the sea water? Yes, the sand of the beach is cleaning the water of the sea continuously. Can you imagine how important is the sand beach? Next summer, when you swim in the clear water of the Mediterranean Sea, remember this. And next night, when you put your hand on the walls of your house, remember what is there inside.