Circle of Life is a beautiful stone-sculpted national garden which commemorates and celebrates the lives and generosity of spirit of organ donors. The garden and park incorporate a rich mixture of Ireland's ancient history and heritage as well as representational stones from throughout Ireland and beyond.

Circle of Life Garden was created by Galway-based charity, Strange Boat Donor Foundation with the support of Galway City in May 2014. It is now one of Galway's leading visitor attractions, and a focal point through which the aims and aspirations of the organ donation community are highlighted and promoted.

While this earth cache brings you to this beautiful memorial, please don't lose sight of the fact that this is a memorial. Family, friends, and recipients of organ donations are visiting alongside you.

A Brief Geology of Ireland

The centre of Ireland is dominantly underlain by carboniferous limestones, which vary from very pure to impure shaley varieties. Within this large area there are two types of rock giving rise to pronounced topographic relief. The first and more frequent consist of Lower Palaeozoic shales and sandstones and Old Red Sandstones. The second consist of younger Carboniferous rocks, predominantly shales, siltstones and sandstones.

The counties Cavan and Monaghan are mainly underlain by Lower Palaeozoic shales, grits and greywackes, whilst counties Louth and Meath are mainly underlain by limestones or marginally younger shales and siltstones.

The South East of Ireland consists predominantly of Lower Palaeozoic sedimentary (mudstones, siltstones and greywackes) and igneous rocks (rhyolites, andesites and basalts). These have been intruded and metamorphosed during the Caledonian Orogeny by the Leinster Granite, which dominates the area’s topographic elevation (Wicklow Mountains).

The South and South West are dominated by Old Red Sandstone and some shales in the west, whilst the easternmost part is more variable with sandstones, shales and limestones occurring in a series of gentle synclines and anticlines formed during the Hercynian Orogeny.

North of these, in northern Kerry, western Limerick and western Clare there are a series of Upper Carboniferous sediments, mainly shales and grits, sitting on top of comparatively pure limestones.

West Galway and West Mayo are characterized by granite in the South (Caledonian Orogeny) and a combination of Lower Palaeozoic and late Pre-Cambrian metamorphic rocks north of this. In the North, most of county Donegal is underlain by a complex series of rocks comprising schists (metamorphosed from mudstones and muddy sandstones), and quartzites (from sandstones). These have been intruded by a series of granites during the Caledonian Orogeny.

Classification of Rocks

Rocks are classified based on the process by which they were formed. There are three rock types: Igneous, Sedimentary and Metamorphic.

Igneous Rocks

Igneous rocks, from the Latin for fire ignis, are formed when molten rock cools and hardens.  Molten rock is called magma when it is below the surface and is called lava when it is above the earth’s surface.

When the magma cools it does so at a slower rate because it is insulated by the surrounding rock. This leads to large grains or crystals being formed; crystallisation. These crystals join together and interlock to form solid rock, usually very hard to break. The crystals are easily seen by the naked eye. Rocks formed beneath the surface are intrusive rocks.

When lava cools on the earth’s surface it cools more quickly which leads to smaller crystals being formed. Rocks formed above the surface are extrusive. 

Igneous rocks may once have been sedimentary rocks or metamorphic rocks before being melted and reformed.  Lots of intrusive rocks are now at the surface in Ireland (including Leinster and Galway granites) due to erosion and uplift.

The upper section of the Earth's crust is made up of around 95% igneous rock.  There are over 700 hundred types of igneous rocks, and they are generally the hardest and heaviest of all rocks.

Some Common Igneous Rocks:

Andesite is an extrusive igneous volcanic rock of intermediate composition, with aphanitic* to porphyritic* texture. It is the intermediate type between basalt and rhyolite and ranges from 57 to 63% silicon dioxide. The extrusive equivalent of diorite is andesite.

Basalt is made of fine-grained interlocking crystals (about 1mm in size). It is black or dark grey in colour, and often contains vesicles (bubbles of gas that got trapped as the lava cooled).

Dacite has an aphanitic* to porphyritic* texture and is intermediate in composition between Andesite and Rhyolite. The word dacite comes from Dacia, a province of the Roman Empire that lay between the Danube River and Carpathian Mountains (now modern Romania and Moldova) where the rock was first described.

Diorite is a medium-to coarse-grained intrusive igneous rock composed of about two-thirds plagioclase feldspar and one-third of dark-coloured minerals, such as hornblende or biotite.  The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. The presence of sodium-rich feldspar, oligoclase or andesine, in contrast to calcium-rich plagioclase, labradorite or bytownite, is the main distinction between diorite and gabbro. Diorite has almost the same structural properties as granite but, perhaps because of its darker colour and more limited supply, is rarely used as an ornamental and building material. It is one of the dark grey stones that is sold commercially as black granite

Dolerite/ Diabase/ Microgabbro is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to aphanitic chilled margins which may contain tachylyte.

Gabbro is a coarse-grained, dark-coloured, intrusive igneous rock. It is usually black or dark green in colour and is composed mainly of the minerals plagioclase and augite. It is the most abundant rock in the deep oceanic crust.

Granite is made of coarse-grained (5mm or so) interlocking crystals. it is a conglomerate of minerals and rocks, primarily quartz, potassium feldspar, mica, amphiboles, and trace other minerals. The relative proportion of different coloured minerals in granite is largely due to the original source of molten rock that cooled to form the granite. The minerals that make up the granite give it its unique colour. If the molten rock was abundant in potassium feldspar, the granite is more likely to take on a salmon pink colour. On the other hand, if the molten rock is abundant in quartz and minerals that make up amphibole, you will likely get a black and white speckled granite commonly seen on countertops. Granite must contain at least 20% quartz. Some black granites are in fact gabbro.  Its extrusive equivalent is rhyolite.

Minerals that give granite its varying colours: Quartz - typically milky white colour. Feldspar - typically off-white colour. Potassium Feldspar - typically salmon pink colour. Biotite - typically black or dark brown colour. Muscovite - typically metallic gold or yellow colour. Amphibole - typically black or dark green colour

Nepheline is the characteristic mineral of alkaline plutonic rocks, particularly nepheline syenites and nepheline gneisses. It occurs in beautiful crystal form with mica, garnet, and sanidine feldspar on Monte Somma, Vesuvius, Italy.

Obsidian, sometimes, when cool, sticky magma erupts, the lava solidifies too rapidly for crystals to form and so volcanic glass is produced. It can have very sharp edges making it useful as a cutting tool or arrowhead.

Peridotite is a dense, coarse-grained igneous rock consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium, reflecting the high proportions of magnesium-rich olivine, with appreciable iron.

Pumice is formed when gas-rich magma froths up and is rapidly blown out of a volcano. The lava is glassy-looking and contains so many bubbles that it is very lightweight, floating on water. Pumice is rhyolite with holes.

Rhyolite is an extrusive igneous rock with very high silica content. It is usually pink or grey in colour with grains so small that they are difficult to observe without a hand lens. Rhyolite is made up of quartz, plagioclase, and sanidine, with minor amounts of hornblende and biotite.  It may have any texture from glassy to aphanitic to porphyritic.

Scoria is a highly vesicular (holy, bubbles trapped…), frothy textured, dark coloured volcanic rock that may or may not contain crystals. It is basaltic or andesitic in composition.

Tuff/ Volcanic Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into solid rock in a process called consolidation. It is a light, porous rock.

A Volcanic Bomb is a mass of molten rock larger than 64 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they are extrusive igneous rocks.

*Aphanitic (from Greek αφανης, "invisible") - igneous rocks that are so fine-grained that their component mineral crystals are not detectable by the unaided eye.   *Porphyritic - igneous rocks with a distinct difference in the size of the crystals, with at least one group of crystals obviously larger than the other.   *Phaneritic - igneous rocks, where the minerals are visible to the unaided eye.

Sedimentary Rocks

Sedimentary rocks are formed from small particles/grains which are eroded or weathered off a parent rock. These grains or sediments are composed of minerals, small pieces of plants and other organic matter. These grains are deposited by water, wind or ice over time, usually at the bottom of lakes and oceans. They are compressed and compacted over a long period of time before consolidating into solid layers of rock, cemented together by minerals such as silica or calcium carbonate. This process is called lithification. These Strata are often seen in exposed cliffs. Sedimentary rocks cover the majority of the Earth's rocky surface but only make up a small percentage of the crust. Sedimentary rocks usually contain fossils. They can be further classified as organic and non-organic.

Some Common Sedimentary Rocks:

Chalk is a soft white limestone made from the microscopic skeletons of marine plankton.

Chert is a hard, fine-grained sedimentary rock composed of microcrystalline/cryptocrystalline crystals of quartz, the mineral form of silicon dioxide (SiO₂). Chert is typically composed of the petrified remains of siliceous ooze, the biogenic sediment that covers large areas of the deep ocean floor, and which contains the silicon skeletal remains of sea creatures.

Claystone is a clastic (rock composed of broken pieces of older rocks) sedimentary rock. It is composed of very fine particles (clay-sized, less than 1/256 mm) which have become cemented into hard rock. Claystone is distinguished from a mudstone by the mudstone's softening upon exposure to water.

Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements; chiefly hydrogen, sulphur, oxygen, and nitrogen.

Conglomerate is made up of rounded pebbles (>2mm) cemented together. They are formed from sediment deposited by fast-flowing rivers or by waves on beaches.

Flint is a hard, cryptocrystalline, sedimentary form of the mineral quartz. It is categorized as the variety of chert that occurs in chalk or marly limestone. Flint was widely used historically to make stone tools and start fires. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.

Greywacke/graywacke is a variety of sandstone generally characterized by its hardness, dark colour, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found in Palaeozoic strata.

Limestone is a common type of carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO). Limestone forms when these minerals precipitate out of water containing dissolved calcium. Limestone often contains fossils, providing information on ancient environments. It often contains variable amounts of silica in the form of chert or siliceous skeletal fragments. Most limestone was formed in shallow marine environments, such as continental shelves. Limestone is exposed at the surface in the Burren.

Limestone is commonly white to grey in colour. Limestone that is unusually rich in organic matter can be almost black in colour, while traces of iron or manganese can give limestone an off-white to yellow to red colour. Limestone is slightly soluble in rainwater (weak carbonic acid).

Common limestone fossils: 1 Trilobite, 2 Colonial Corals, 3 Colonial Corals, 4 Solitary Coral, Siphonophyllia, Cross Section, 5 Solitary Corals, 6 Crinrod, 7 Gastropod, 8 Bryozoan Colony, 9-11 Brachiopods

Mudstone is made up of fine-grained clay particles (<0.05mm) compressed together. Mudstones form where clay has settled out in calm water - in lakes, lagoons, or deep sea. Flaky mudstone is called shale.

Sandstone is made of sand grains (0.05-2mm) cemented together. It is formed from sediment deposited by rivers, the sea, or by the wind. There are many types of sandstone. They make up about 20 - 25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface Sandstone may be any colour due to impurities within the minerals, but the most common colours are tan, brown, yellow, red, grey, pink, white and black.

Metamorphic Rocks

Metamorphic rocks were once igneous or sedimentary rocks, but have been changed due to intense heat and/or pressure within the earth’s crust, usually the result of intense tectonic activity.  This process, called metamorphism, does not melt the rock but changes the rock by growing new crystals from the original composition of the rock.

Uplift and erosion help bring metamorphic rock to the Earth's surface. Often the crystals lie in a particular direction, due to the pressure, and the rock looks like it was squashed. 

Some Common Metamorphic Rocks:

Anthracite is a type of coal with a high carbon count, few impurities and with a high lustre.

Gneiss is made of coarse-grained interlocking crystals. Crystals line up in pale and dark layers to give the rock a banded texture. Formerly Granite.

Granulite is a metamorphic rock that is formed from the igneous rock Basalt.

Marble is made of calcium carbonate (fizzes with acid). It has medium-grained interlocking crystals with no alignment. Formerly Limestone.

Quartzite is formed when quartz-rich sandstone or chert has been exposed to high temperatures and pressures. Such conditions fuse the quartz grains together forming a dense, hard, equigranular rock.

Schist is made of medium-grained interlocking crystals. Its shiny appearance is due to the mineral mica. Crystals line up to give the rock wrinkly layers – this is called foliation. Formerly Mudstone or Shale.

Slate is made of fine-grained interlocking crystals which lie flat in the same direction, known as the cleavage direction, along which the rock easily splits. Formerly Mudstone.

The oldest known Irish rock is found on Inishtrahull Island off the north coast of Ulster. The island is formed of granitic gneiss, a type of metamorphic rock known as Inishtrahull Gneiss. It is dated at 1.7 billion years old, making it Paleoproterozoic in age.

Sources:

https://www.teagasc.ie/media/website/publications/2011/Soil_Geochemical_AtlasofIreland.pdf

https://www.gsi.ie/en-ie/education/rocks-minerals-and-gems/Pages/Rock-types.aspx

To log a find:

Task One:

This earthcache will focus on one rock from each Province.

1. Ulster - Giant’s Causeway, Antrim
2. Munster - Charlesfort, Cork
3. Leinster - Brownshill Dolmen, Carlow
4. Connaught - Dún Aonghusa, Galway

For each province/county please identify the rock in question and list the following characteristics.

a) Name b) Classification c) Is it considered a hard/soft rock? d) Colour e) Texture f) Grain size g) During what period was this rock formed?

Task Two: answer these questions.

Question Two

2.1 One of the rocks mentioned is mafic. Which one?

2.2 One of the rocks mentioned is felsic. Which one?

2.3 Explain the process of lithification. 

2.4 Which of these rocks I – IV, if any, underwent lithification? 

2.5 In your opinion, why do Sedimentary rocks only make up a small percentage of the Earth’s crust compared to metamorphic and igneous types of rocks? 

2.6 Which of these rocks contains CaCo3?

2.7 Which rock is an inorganic sedimentary rock? 

2.8 Sedimentary rocks can be further classified as organic and non-organic. Give some examples of each found in Ireland today. 

2.9 Explain the process of crystallisation. 

2.10 What is the oldest rock found in Ireland?

2.11 And an easy one for the road … What is the difference between magma and lava?

Task Three:

3.1 To prove you visited please add a photo of you/your GPS at the Circle of Life park in general to your log.