GEO GARDEN

I studied Geology at the University of Manchester from 1969 to 1972. I taught A level geology at Marple Hall School and the Cheadle & Marple 6th Form College until 2006. I am now retired but still interested and curious about geology.
In recent weeks I have created a geology rock garden from my collection of rocks, fossils and minerals. Both children and adults are fascinated by the “short” descriptions and stories about my rock collection.

Geology Rock Garden
Sedimentary Rocks
1 Sandstone – Showing flute casts, turbidity current gouging of muddy sea bed, infilled with sand latter lithified
into sandstone. The sedimentary rock comes from Mam Tor, located in the Peak District and is made up of rocks
formed during the Upper Carboniferous Period, roughly 320 million years ago.
2 Conglomerate – a rock composed of rounded pebbles and sand.
3 Limestone – This a sedimentary rock made from the fossilised remains of colonial corals that lived in the Lower
Carboniferous times around 350 million years ago in shallow tropical seas.
4 Limestone – Cotswold Stone. The rocks that form the Cotswolds are from the Jurassic period and date from
between 210-140 million years ago during the Jurassic period. You can see fossil brachiopod shells and some
crinoids (sea lilies).
5 Travertine – is a sedimentary rock, specifically a form of terrestrial limestone. It’s formed by the precipitation of
calcium carbonate, often around hot springs.
6 Flint – Flint occurs mainly as nodules and found in layers in sedimentary rocks, such
as chalks and limestones. Inside the nodule, flint is usually dark grey or black, green, white, or brown in colour,
and has a glassy or waxy appearance. A thin, oxidised layer on the outside of the nodules is usually different in
colour, typically white and rough in texture. This sample is from the Chalk beds in the Cretaceous period – 143 to
66 million years ago. One theory of their origin is that they are made from the silica within some sponges on the
seabed.

Igneous Rocks
10 Granite – Shap Granite. Granite is an intrusive, felsic, igneous rock. It is formed from slow cooled magma deep
within the Earth’s crust, resulting in a coarse-grained texture with visible mineral crystals. Granite is composed
primarily of quartz, feldspar, and mica. In this sample you can see large crystals (phenocrysts) of pink orthoclase
feldspar. The age of the rock is 393 million years from the early Devonian period. Shap granite is named after the
village of Shap in Cumbria, England, where it is quarried.
11  Granite – Grey Granite. Crystalline intrusive igneous rock made of quartz, feldspars and mica
12  Orbicular Granite – Orbicular granite is a rare and visually distinctive type of granite characterized by the
presence of orbicular (rounded) structures or concretions within the rock matrix.
13  Granite – Grey granite with large phenocrysts of white orthoclase feldspar. From Cornwall and formed about
280 million years ago from slow cooling deep seated magma.
14  Larvikite – is a black igneous rock made up mostly (90%) of feldspar that crystallizes in the form of large crystals.
Within the feldspar itself, there are small silver-blueish shimmering crystals that give Larvikite it’s eye catching
“flash” referred to as the “Schiller Effect”. Larvikite is believed to have formed over 298 million years ago. The
name of this mineral comes from the local town of its original discovery; Larvik, Norway.
15  Basalt – a black / charcoal grey fine grained extrusive igneous rock. This sample was collected from the sea bed
near to the mid Atlantic Ocean Ridge by a geological research ship.
16  Ignimbrite – Ignimbrite is a type of volcanic rock, consisting of blobs of volcanic ash and lava that settle and
during compaction deform into elongated shapes.
17  Volcanic Lava Bomb – from the Auvergne, France. The sample is from volcanic activity occurring between 45,000
million years and 30,000 million years ago.

Metamorphic Rocks
20 Slate – Slate is a fine-grained, metamorphic rock that is created by the alteration of shale or mudstone by low
grade regional metamorphism. It easily splits along cleavage planes into sheets and It is popular for a wide variety
of uses such as roofing, flooring, and flagging. This sample from north Wales shows a former bedding plane and is
of Ordovician age.
21 Mica Schist – Schist is a medium-grained strongly-foliated crystalline metamorphic rock, formed from highly
deformed sedimentary rock during mountain building. This sample has large sheets of mica
22 Shist – Green schist from Anglesey
23 Marble – Marble is a metamorphic rock made from crystallised limestone.
24 Quartzite – Quartzite is a naturally formed metamorphic rock, primarily composed of quartz, that results from
the metamorphism of sandstone
25 Gneiss – a metamorphic rock with a banded or foliated structure, typically coarse-grained and consisting mainly
of feldspar, quartz, and mica
26 Migmatite is a large scale banded metamorphic rock. It consists of darker basaltic bands and lighter granitic
parts. This sample is from western Scotland.

Minerals
30 Amethyst – Amethyst usually is a transparent variety of quartz that comes in shades of purple. This sample also
contains cubic crystals of Galena
31 Galena – Galena is specifically lead sulfide (PbS), and is the most important ore of lead. Galena’s density is
around 7.4 g/cm³. This sample comes from The Peak District, Derbyshire.