Welcome to lecture seven Part 2.

Here we will look at Pleasure Place helper, feldspars and their properties.

As crystals.

And their composition is a family of solid solution minerals.

We will also.

Learn to understand phase diagrams related to changes in the composition of feldspars. Next week, we'll take this further and we will look at the properties of fast bursts in thin section. How to recognize them and what their meaning is in terms of rock history.

Pleasure clays minerals have a general chemical formula reported.

I'm at the top here.

Whereby there is the substitution of calcium and sodium indicated here is WX.

And then there are YNZ, which are the cations they occupy. The center of the tetrahedron structure.

And then there's the oxygens pleasure clases triclinic in symmetry and the two and members are. I'll bite and annotate, I'll bite, contains 100%. So sodium anorthite contains 100% calcium. There is also a different in the aluminium content there is more Silicon and aluminium in albite, whereas in a Northside the aluminum content goes up.

The type of composition of variations seen in the pleasure place family is known as solid solution and sodium and calcium can substitute substitute for each other in the same lattice site and they can coexist together in various proportions as a continuum in plagioclase minerals and silicone substitutes for aluminium.

What is the relationship between these substitutions? Let's have a look at some phase diagrams.

So this is a phase diagram which reports temperature on the Y axis and the composition of the pleasure place on the X axis, ranging from zero calcium to 100% calcium. The diagram is.

Represented at a constant pressure of 1 bar.

We can draw up two lines within the diagram. One is known as the liquidus.

Above, which here everything is a liquid Teresa is amount. We can also draw line which is known as the solidus, and below this line in this field. Here everything is a solid. Now between the Liquidus and solidus lines, both crystals and melt coexists together.

Now, in order to understand how a phase diagram can be read and is useful, let's represent a given liquid of composition of 50% sodium and 50% calcium in a pleasure place.

And also, let's assume that this composition is there above 1500 degrees C's.

So.

As this melt cools down, it will reach the liquidus line and.

The composition of the melt on the Liquidus line still reads 50% calcium, 50% sodium.

But when we hit the liquidus, a solid face forms and the composition of the solid face, which would be a crystal of pleasure, clays.

Must be red on the solidus line, so we must draw a line parallel to the X axis. The hits the solidus line there and the composition is red off the bottom here.

I'm on the X axis, therefore the first pleasure placed to form.

In the white area.

Contains very high calcium, about 80% and it contains 20% sodium.

This crystallization of the first pleasure place causes the residual melt to be depleted in calcium and therefore now the composition of the melt moves down on the X axis, and it will be around here. If the cooling process continues from 14150 degrees, is downwards up, 1400 degrees sees we read the composition of the melt.

In the position indicated by the next green ball, which I'm highlighted with the cursor.

And that melt contains 30% calcium and 70% Sergio.

Here again, we have crystallization of a solid phase in the form of blood euclase crystals, the composition of which must be red on the solidus line. Therefore, we extrapolate horizontally until we hit it, and then we read the composition of the solid down here and this pleasure place. This time contains 70% calcium and 30% Sergio.

Again, the formation of plunger clays has depleted the residual melt of more calcium and therefore we have a further change in composition of the melt, which moves further down the X axis or kupine more or less this position. Now over here.

So from here.

If we.

Further called the system down.

We have a composition of melt of about 10%.

Calcium and 90% sodium.

And from this melt we have the crystallization of plagioclase of composition red from the solidus.

To be around 50% costume and 50% Sergio.

This again we have changed the composition of the melt further.

And further down the X axis in this position.

As the system continues cooling down.

We have

crystallization of.

More pleasure clays, which this time will have composition 30% calcium and 70% Sergio.

Now through this process, the pleasure Klees grows as a zone crystal.

And we can see it in the image on the left hand side on this slide, whereby the pleasure place grain.

Is indicated by the red arrow here, and you can clearly see that it shows chemical zoning, so the areas of different extension or different coloring are the areas grown as zones of potentially decreasing.

Calcium content, for example, from a calcium rich coal to a calcium poor rim.

Now the blue arrow.

Is pointing at a completely different mineral and I will leave you to describe the properties of these minerals and identify it.

Generally.

With the picture on the right hand side, I wanted to show you what pleasure clays really looks like in a thing section. It is strongly characterized by very.

Recurrent polysynthetic albite twinning.

Which is described by this alternating light and dark stripes, which are set of Twins that go into extension at different times.

To be noted is the untighten albite, the two and members have actually.

All optical properties in common. The only one distinction that we perhaps can make is the unauthorized often grows chunkier. Polysynthetic albite Twins, whereas albite tend to grow them a lot thinner.

And here have reported for you the reading list for week seven entities focused around the properties of quartz and pleasure place files. But do not forget an incredible amount of information is provided to you via the Mineral Handbook, and in particular, these minerals are described in practicals. D&E.

Also look at the handouts they have published in campus for this week and.

For our preferred textbooks, I've indicated the key chapters to look at.

As well as the key pages to look at in the Atlas of Rock forming Minerals.

Next we will go through lecture 8.