I had planned a new excursion to a nice little village today, but since it’s rainy and gloomy, I have procrastinated the visit and taken the opportunity to do some needed research about the types of stones used in memorial stonemasonry.

Sandstone

sedimentary rock made of sand grains eroded from rocks and cemented together. Grains are quartz, the cement can be iron oxides / calcite / silica.

colour: buff, red, grey

gravestone uses: unpolished, affords deep carving

decay: can be eroded / can be totally covered by lichens

Gritstone

sedimentary rock that can be mistaken by sandstone, but it has grains are larger and less rounded than in sandstone.

Limestone

It contains marine fossils and is mainly composed of calcite.

colour: commonly white, light grey, buff, pinkish white, but can also be dark grey.

gravestone uses: unpolished.

 

 

 

i.e. cliffs of Dover, Seven Sisters (South Downs near Brighton) are made of limestone

Slate

methamorphic rock (from mud) with a multi-layered structure, commonly used for roofing.

colour: medium/dark grey, but can also be buff or green. 

gravestone uses: unpolished / shallow carving and crisp lettering

decay: not totally covered, but easily splitted.

Marble 

 white sugary, vaguely luminous methamorphic rock derived from limestone. It is mainly made of calcite (like limestone), sometimes with grey mineral veins.

colour: white, sometimes with grey mineral veins. running through the stone.

gravestone uses: unpolished and polished 

decay: polished marbles are not very resistent. Marble can be easily stained. Look at the joints (i.e. where it attaches to the wall) to determine its original colour.

A common weathering agent of decay is acid rainfall, which roughens the marble’s surface.

Granite

ingneous rock, marked with chrystals that look like spots. Main minerals:

feldspar, which gives it its colour

quartz (greyish, glassy chrystals)

mica (grey or brown-black glittery crystals)

crystals are in random arragement.

colour: pink, dark grey

usually polished, but also unpolished

decay: can be obscured, but not totally covered

 

Dolerite

similar to granite, but it is black (also called “black granite”). 

 

Gneiss

metamorphic rock, similar in appearance to schist, but with distinct alternate bands.

Schist

foliated metamorphic rock, with parallel layers similar to slate, but its grains are apparent under lens, whereas in the latter they are too small to be seen.

 

Gabbro

similar to granite, but with patchy rather than speckled surface and 50:50 of dark and light crystals.

 

 

Legend

sedimentary rock: rock made up (70%-80%) of sediments (fragments from other rocks) compacted together

igneous rock: rock made of solidification of cooled magma

metamorphic rock: transformation of an exhisting rock under heat and pressure to another