Learning geology from buildings in downtown Toronto

Saturday, May 24, 1997

Kathleen Kemp, Tucker Barrie, Marcia Charles, Janet Parkin, Denise Payne and Michael Perkins


Most building stones in Toronto are of igneous or sedimentary origin, but metamorphic rocks are also represented. Intrusive igneous rocks have a coarse inter-locking texture; they are durable and polish well. Sedimentary rocks are generally softer and more porous; they are commonly used for ornamental purposes such as carved entablatures over doorways or fluted columns. Metamorphic rocks are represented by a variety of marbles and gneisses, and are generally used as polished facing stones on interior and exterior walls.

The Queenston Limestone and the Medina Sandstone are the most common local rocks used as building stones in Toronto owing to the proximity of their quarries in the Niagara Escarpment. The rock known as the Queenston Limestone (which is actually a dolostone) caps the Niagara Escarpment and is quarried in Hamilton, near Niagara Falls and in Collingwood. This stone is light brown to buff coloured, sometimes cross-bedded, well cemented, free of jointing, and is ideally suited for building purposes. You will see the Queenston Limestone at the Royal Ontario Museum.

The Whirlpool or Medina Sandstone, part of the Clinton Group is quarried along the Escarpment from Hamilton to Orangeville, just to the west of the Queenston outcrops. It is a multicolored, well cross-bedded quartzose sandstone. Its predominantly quartz cement makes it durable. "Red Medina" was quarried at the Forks of the Credit River in the 1880's for the original portion of the provincial parliament buildings and the old city hall. Both red and grey varieties were used at the Royal Ontario Museum.

Notable examples of sedimentary stones that come from outside Ontario include the following:

  1. Tyndall Stone from Manitoba, a unique tapestry stone consisting of grey limestone with light brown dolomitized burrows and large, well preserved fossils of coral, snails, nautiloids etc. (eg., College Park, 444 Yonge Street);
  2. Indiana (or Salem ) Limestone, a uniform, fine-grained grey to beige limestone composed of small discs from fossil crinoids. The Indiana Limestone is often used as trim on buildings made of brick or other types of stone (eg., Royal Bank on tour);
  3. the Ohio Sandstone, another durable quartzose sandstone that withstands chemical weathering (eg., carved entrance to University College).

Today, over 90% of the building stone quarried in Canada is igneous rock from Quebec. The common (although inaccurate) construction term for all coarse-grained igneous rocks is granite; composition is distinguished by colour and has lead to popular terms such as black granite or pink granite. In Quebec, pink granite (K-feldspar porphyritic granite), black granite (gabbro and anorthosite), and brown granite are quarried. In Ontario, pink K-feldspar granite from Vermilion Bay (near Dryden) and a grey gabbro from north of Sudbury are quarried. These rocks are cut into slabs or monuments, rough polished on site, and then shipped to Quebec or Vermont for polishing.

A greater and greater number of metamorphic rocks are being used as building stones in Toronto. They come from places around the world including Vermont, Italy and India and include many types of marble, green serpentine marble, and several types of gneiss. Some striking Ontario marbles from Bancroft are showcased in the rotunda of the Royal Ontario Museum.

Decay of stone

The combination of salt and moisture is particularly destructive to sedimentary rocks which tend to be porous. Water dissolves salt (present in the rock or introduced from de-icing salt or mortar) and carries it through minute passage ways in the stone. The salt may be deposited at the surface of the stone causing unsightly white blotches or margins (called effloresence). Salt may also be deposited just below the original stone surface (subfloresence). The salt loosens the original surface and it peels off.

Limestone is slightly soluble in water; the solubility increases as the acidity of water increases. Carbon dioxide, sulphates and nitrates produced by car exhaust, burning coal to generate power and incineration combine with rain water to form more acidic rain which dissolves limestone. Some components of a stone (eg. fossils) may be more resistant to dissolution and stand out in relief as the rock around them is dissolved; this is an example of differential weathering. Frost action (expansion of water du ring freezing) is responsible for separation along clay layers. Water adheres to clay particles and cannot easily move through the clay as it freezes and its volume increases. A complete discussion of the types of decay that affect building stone can be found in Winkler (1975), Chapter 5 "Decay of Stone".

Industrial minerals

Each year every person in North America "consumes" 11 tons of non-metallic earth materials, such as lime, sand and gravel, and stone and 2/3 of a ton of metallic minerals such as iron, steel, copper, lead, zinc, and aluminium. The non-metallic minerals such as calcite, quartz, glauconite, graphite, iodine, feldspar, phosphate, sulphur, and wollastonite are called industrial minerals because they are generally used during industrial processes as catalysts, thickeners, extenders, fillers, and brightening a gents. The most common industrial, mineral, lime is used in cement. Lime (CaO) is derived from the mineral calcite (CaCO3) which makes up limestone by crushing and heating to drive off carbon dioxide gas (CO2). As lime is unstable at normal temperatures and will reabsorb carbon dioxide, water is added to produce hydrated lime which is more stable and results in a longer shelf life. A recipe for cement is "2 cups crushed limestone, 1/2 cup clay, mix thoroughly, grind up fine, bake at 1427°C, cool, add 1 teaspoon gypsum, and grind very finely." (Bates and Jackson, 1982). North Americans use 90,000,000 tons of cement each year. The production of every ton of lime requires 1750 Kwt and produces 3/4 ton of carbon dioxide. Cement is mixed with gravel, sand, and water to produce concrete.

Another product that contains cement is terrazzo. Terrazzo is composed of equally sized blocks, usually of marble or limestone, mixed with cement, poured for flooring and then smoothed. Terrazzo can be distinguished from natural stone by the consistency in size of the rock chips and the very fine-grained matrix. Terrazzo does not have veins that are commonly found in marbles.

While the industrial minerals that are used most commonly are aggregates and cements most products contain industrial minerals. Glass for example, is composed of silica from quartz (SiO2). Fine-grained silica sands (70%) are mixed with sodium carbonate (15%) limestone (7%) and nepheline syenite which lower the melting point of the silica from 1700°C to as low as 600°C. The addition of borax produces Pyrex ovenware glass. Additives and the colours that they produce include: sulphur (amber), selenium (pink), cobalt oxide (blue), iron oxides (green, yellow, and brown), and fluorite which is used to make glass opaque. Other additives are used to improve viscosity, correct for impurities, and reduce bubbles in the glass.

Gypsum (CaSO4 · 2H2O), a mineral used in cement to control drying time, is commonly seen in the form of plaster of paris and drywall. Gypsum is formed by the evaporation of seawater. When heated gradually from 120°C to 205°C gypsum loses 3/4 of the water in its chemical structure. When the water is restored the gypsum crystals reform making a firm material. Drywall, sometimes referred to as gyprock, is composed of a layer of gypsum sandwiched between two paper layers.

Most industrial minerals have many uses. Sulphur (S) comprises 0.06% of the Earth's crust and is found associated with gas and oil deposits, mineral springs, salt domes, evaporite basins and as a byproduct of many refining operations. Sulphur is used in almost every industrial process. Most sulphur is converted into sulphuric acid which is then used in the production of fertilizers, explosives, synthetic rubber, batteries, aviation gasoline, antiknock gasoline, tires, acetate, cellophane, photographic fil m, iron, steel, tin, galvanized products paints, enamels, linoleum, paper, ink, livestock feed, magnesium, aluminum reduction, etc.

Over 50 types of industrial minerals are currently being mined throughout the world. Industrial minerals are a 1.5 billion a year industry in Ontario where about 10 types are produced in addition to aggregates such as gravel, dolomite, limestone and quartzite. Other industrial minerals produced in Ontario are: salt, nepheline syenite, gypsum, talc, yttrium oxide, barite and serpentine.

Our tour begins at the Royal Bank located beside the St. George exit from the St. George Subway Station.

Stop 1: Royal Bank
264 Bloor Street West

The polished grey-blue stone used around the entrance and windows of the Royal Bank is composed mainly of grey feldspar. Feldspars are the most common minerals found in the earth's crust. Feldspars consist of the elements silicon, oxygen and aluminum and are sub-divided into different mineral species on the basis of the amount of calcium, potassium and sodium that they contain. They are usually pink or off-white in colour but can be grey to black in colour as seen here. These feldspars are rich in calcium and are known as labradorite and the rock composed dominantly of these feldspars is an anorthosite. The colours reflected from the surface of the labradorite crystals change from blues to blacks as you move your head about. Slightly different compositions of feldspar that have separated from one another during the solidification of the rock form fine alternating layers. Each composition influences light differently creating an attractive play of colours which is exploited as a gemstone in similar material mined from Labrador, Canada. Metallic steel-grey flecks of the mineral magnetite can be most easily seen by looking up along the surface of the rock. As magnetite's name suggests it is strongly attracted to a magnet. When magnetite is found in large quantities it is mined as a source for iron. The stone's glossy surface has been achieved by polishing the rock with a very fine abrasive and not by coating it with a varnish.

Anorthosite is an example of an igneous rock, that is it formed by the solidification of magma. In this case magma cooled slowly enough for the crystals to grow to a size that is large enough for us to see without the aid of a magnifying glass. This slow cooling takes place when magma is insulated by over-lying rocks and results in minerals that have actually grown into one another.

The outside walls consist of crinoid-packed Indiana Limestone, Crinoid fossils look like cheerios in cross-section and somewhat like stacked vertebrae when sliced along the length of one of the columns. They belong to the same phylum as starfish and some times you will see a five-rayed star rather than a round hole in the centre of one of the "cheerios". Some limestones are examples of a sedimentary rock that was formed from chemical derived from the weathering (or breakdown) of a pre-existing rock. The predominant mineral making up limestone is calcite which is composed of calcium, carbon and oxygen. This limestone was produced by crinoid animals when they grew. Walk east along Bloor Street and south on Queen's Park road to reach the entrance to the Royal Ontario Museum.

Stop 2: Royal Ontario Museum, 
100 Queen's Park Road

Like most older "stone buildings" in Toronto the museum is a brick building with a layer of natural stone on the surface that is usually about 10 cm thick. In modern buildings thin slabs of stone (3 to 4 cm thick) are hung on the building. Stone not only creates an attractive appearance but typically provides a lasting finish that requires little maintenance and some insulation.

The lower part of the building exterior including the carved stone by the entrance is Queenston Limestone, the local crinoid-packed stone which is very similar to the Indiana Limestone seen at the Royal Bank. Occasionally you will see a fossil that looks like a shreddie which is the remains of a colonial animal known as a bryozoan. Notice that the fossils tend to stick out because they are more resistant to weathering than the rest of the rock. Most of the exterior wall facing Queen's Park Road is finished with the grey variety of the Whirlpool Sandstone. The red stone that is used to create decorative accents comes from the same formation and owes its red colour to the presence of the mineral hematite (an iron oxide) which stains the grains of quartz that comprise the stone. Sandstones are sedimentary rocks that are made of pieces of pre-existing rocks that have been weathered and then cemented (or glued) together. If you run your hand along the surface you can feel that the grains of quartz feel like sandpaper. Quartz is a hard mineral and is used to make abrasives such as sandpaper. The strength of the rock is controlled by the nature of the cement holding the grains together.

Inside the front entrance, on the floor of the rotunda (or lobby) pink, buff and white brecciated marbles from the area around Bancroft have been used to create a mosaic. Breccias consist of large angular fragments that have been glued together by a natural cement introduced by water traveling through the stone. Marbles are metamorphic rocks that have been formed from pre-existing rocks by exposure to high temperatures and/or pressures. The original rock that is metamorphosed or "changed" into marble is limestone. As a result marble like limestone, is composed of calcite. The various colours of marble are the result of trace impurities found in the stone. In the centre of the Rotunda floor is a star composed of the blue mineral sodalite with some pink cancrinite. The sodalite comes from Bancroft which is a world-famous locality for this mineral.

Continue south then cross Queen's Park Road and go through the park to reach the legislative buildings.

Stop 3: Ontario Parliament Buildings, 
Queen's Park Crescent

The main building is constructed of large blocks of the red Whirlpool Sandstone quarried near the Forks of the Credit and Orangeville. Most of the Whirlpool sandstone consists of horizontal sedimentary layers or beds but careful inspection reveals portions of the rock where the layers are at an angle to the horizontal. This is known as cross-bedding and was produced when water or wind currents moved sand grains about creating ripple-like structures that had surfaces that accumulated sediment at an angle other than horizontal. Occasionally the outlines of ripples, like the ripples you might see on a beach on a river bottom, can be seen.

The west wing, which was destroyed by fire in 1909 was rebuilt using red sandstone from Sackville, New Brunswick since the Credit Valley quarries were virtually exhausted by this time. The Sackville Brownstone was used again when the north wing was added in 1913. The Sackville Brownstone is a lighter colour of red and does not contain cross-bedding. Neither the Whirlpool nor Sackville sandstones weather well where they are exposed. They require restoration on an ongoing basis.

You may observe white deposits of salt on the sandstones due to efflorescence. These deposits form when salt used to melt winter ice forms a brine which is drawn up through the porous and permeable sandstone and deposited on its surface. Surface deposits such as this may be unsightly but they do not damage the stone. In contrast when salt crystallizes under the surface of the rock it can destroy the cement gluing the sand grains together and cause the rock to fall apart. By comparing the carved sandstone which is protected by a roof with the stone that is exposed to rain you can see that the protected carvings are much crisper than those that have been exposed. This is an example of the results of slightly different micro-climates.

The roof is a blue slate which was quarried in Rutland, Vermont, USA. Slate is a metamorphic rock that consists of tiny flat minerals that grow at 90° to the direction in which they are being squeezed. This results in its tendency to split in flat layers: - a tendency exploited when slate is used to make roofing shingles, billiard table tops and blackboards. Marble used in the interior of the west wing is from Italy. Unfortunately, the fanciful notion that this marble contains dinosaur bones is untrue.

Return to the north side of Bloor Street and walk east to the Air Canada Building.

Stop 4: Air Canada Building, 
130 Bloor Street West

The exterior of the building is covered with a light-grey gneiss. Gneiss (pronounced "nice") is a metamorphic rock that is characterized by bands of different mineral compositions. The weakly developed bands in this rock consist of dark-coloured minerals (such as biotite and hornblende) alternating with light-coloured minerals such as quartz and feldspar. The original rock may have been an igneous rock such as a granite or a sedimentary rock such as a sandstone that contained minerals other than quartz.

The interior walls near the elevator are finished with a polished orange coloured marble which is cut by white calcite veins. The calcite in the veins was probably derived from the surrounding rock and filled in fractures or cracks in the rock. The floor also consists of marbles which are white with grey "marbling".

Back-track to the lights at Queen's Park (or Avenue Road) and Bloor and cross to the south side of Bloor. Walk east to the Colonnade.

Stop 5: The Colonnade 
131 Bloor Street West (just west of Avenue Road)

The Colonnade was the first building in Canada, and one of the first in the world, to combine residential, commercial uses. The 12-storey building is almost entirely composed of reinforced concrete and stands out as a commemorative grey monument of the profitable times of the sixties. It can be recognized by the distinctive free standing spiral staircase located in its forecourt. The staircase is composed entirely of manufactured stone (often referred to as concrete). Relatively large pebbles set in t he matrix of finer ground material are easily visible. A benefit of using manufactured stone (concrete) is that it can be produced to match any structure already present.

The exterior walls of The Colonnade are finished with a polished pink granite called the Rapakivi Granite. Granites are slowly-cooled igneous rocks containing feldspar, quartz and another mineral. The rapakivi granite is characterized by rounded potassium feldspars (which are pink) surrounded by a rim of green feldspar plagioclase (which contain sodium and calcium rather than potassium). The rock also contains quartz (grey and white coloured material with an irregular shape) and darker coloured grains are the amphibole, hornblende. Minor amounts of the black mica, biotite, are also present. The dark colouring of biotite and hornblende is due to the presence of iron and/or magnesium in the minerals. "Rapakivi" means "rotten stone," and refers to the tendency of different parts of the stone to weather at different rates. Fortunately the break down of Rapakivi granite takes place on a geological time scale and is insignificant on a human time scale.

The roughly finished square pavers used on the ground outside the Colonnade are also made of granite. Here the large pink feldspars have a more typical rectangular shape and have no rim. The interior floor of the front entrance lobby consists of agglomera ted pink- and buff-coloured tiles that are the manufactured equivalents of brecciated marbles. The tiles are made by breaking limestone into large pieces and using a mixture of epoxy and the finer material to glue the rock together. The interior walls are decorated with polished, buff coloured travertine limestone. Travertine forms around hot springs and consists of characteristic wavy layers of fine-grained calcite that were trapped by cynobacteria or blue-green algae. Large holes or pores are another characteristic feature of travertine, and are often, as they are in this case, filled in with epoxy to make the rock easier to clean and more resistant to wear.

Continue walking east on the south side of Bloor Street to the Manulife Centre.

Stop 6: Manulife Centre, 
55 Bloor Street West (encompasses the entire city block bounded by Bloor, Bay, Charles, and Balmuto streets)

Like The Colonnade, the Manulife Centre is a multi-purpose building, and like The Colonnade, the Centre is a solid mass of concrete. The building exterior consists of manufactured stone. The exterior and interior round pillars allow one a close inspection of the concrete. The pebbles (or aggregate) found in this manufactured stone are much smaller than those seen at The Colonnade.

The interior lobby floor contains an intricate patterning of three different agglomerated marbles, which are similar to a natural breccia. To the left of the east revolving door entrance, one can clearly see the result of the wear and tear on the stone by the traffic of people in and out of the Centre. Here the matrix has been weathered down and lost its smooth polished texture; the angular pieces are more resistant and remain unharmed and now jut out above the matrix.

The interior walls, located inside the Centre past the Bank of Montreal are finished with two distinct igneous rocks. The stones are displayed in an alternating pattern of dark and light in narrow and wider slabs. The dark rock is another example of anorthosite containing labradorite with its distinctive irridescence. The lighter granite (more precisely a granodiorite) is rich in plagioclase feldspars, quartz, hornblende, and minor biotite. Farther into the mall some of the pillars and portions of the walls are finished with a dark brown limestone that contains poorly preserved rugose coral. The two-dimensional sections that you see cut across the horn-shaped fossils of this now extinct group of coral. Some cross-sections will be round to oval, some conical and others a combination of the two. Sometimes you can see the internal divisions or septa within the coral extending to the outside of the horn.

Continue walking east on Bloor Street to Stollery's.

Stop 7: Stollery's, 
1 Bloor Street West (South-west corner of Yonge and Bloor Streets)

The exterior wall below the display windows shows an example of serpentinite. Serpentinite is composed of green minerals that originally crystallized at high temperatures and are now meta-stable at the temperatures that exist on the earth's surface. Hot water solutions cut through the rock and accelerated the conversion of the grains to new minerals that are stable at surface temperatures. Fibrous minerals such as the ones seen in these light-coloured veins are described as having an asbestos shape or hab it. Most of the asbestos minerals have since been replaced by white calcite which has kept the fibrous texture. This rock was formed on the ocean floor and got "stuck" onto the over-riding continental crust as oceanic crust subducted beneath it.

Cross Yonge Street and continue walking east to the Xerox Building located at the entrance to the subway.

Stop 8: Xerox building, 
33 Bloor Street East (Just east of Yonge Street)

Approaching the Xerox Building from Yonge Street the first entrance encountered is one that leads to the subway. Here the exterior walls are finished in the igneous rock, Lake Placid Anorthosite. The minerals present include large labradorite and black hornblende crystals. The stone was laid in alternating polished and unpolished slabs producing distinctly darker and lighter bands from the same stone. The interior floor of the subway entrance is composed of terrazzo consisting of black rock chips embedded in a green cement.

At the main entrance to the Xerox Centre the exterior walls are finished with polished stone. If you look carefully at the stone you can see gold metallic specks. These flecks are particularly notable in the middle pillar below the building number. These spots are not actual gold but are a sulfide mineral such as chalcopyrite (copper pyrite). The steps and outside landing have been covered with roughly finished anorthosite which provides traction for pedestrians even when the stone is wet.

Suggested further reading

Bates, R. and Jackson, J, 1982, Our Modern Stone Age, American Geological Institute.

Fouts, C.R., Freeman, E.B., Kemp, K.M., Marmont, C. and Minnes, D. G., 1991, Building stone and Historic Structures in Downtown Toronto, Geological Association of Canada, Toronto '91, Field Trip A11/B11 Guidebook.

McKelvey, M. and McKelvey, M., 1984, Toronto: Carved in Stone, Fitzhenry and Whiteside, Toronto.

Winkler, E.M., 1975, Stone: Properties, Durability in Man's Environment, Springer - Verlag, New York.