3 Physical properties of minerals in hand specimen

Physical properties, such as colour and density, are those that can be observed without causing any change in the chemical composition of a specimen, whereas chemical properties determine how a substance behaves in a chemical reaction. Many of the physical properties of minerals can be predicted from a detailed knowledge of their crystal structures, which can be obtained by various analytical techniques. Alternatively, physical properties can be used to infer particular aspects of a mineral's internal structure.

Several physical properties of minerals can be readily observed in hand specimen and can be used for recognising and distinguishing different minerals. In this course you will do this using the Digital Geology Kit [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , which is introduced in the next activity.

Activity 1 Introduction to the Digital Geology Kit

Timing: Allow about 40 minutes.

Task 1

Begin by watching Video 1 to familiarise yourself with the functionality of the Digital Geology Kit. (You will need to view it in 'Full Screen' mode in order to see in detail the various tools and features.) Then answer the associated questions.

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Transcript: Video 1 Introduction to the Digital Geology Kit.

Instructor

The Digital Kit is a system for viewing and exploring geological hand specimens, using a web browser. This tutorial will show you what it can do and how to use it. The screen is divided into the field of view of the specimen and several functional areas that control the images, including a main viewing window; zooming facilities; buttons or links to other images, video clips and mineral properties.

In the upper right-hand corner, a catalogue of specimens can be accessed via two drop-down menus. Click the upper menu to select from the categories of minerals, rocks or fossils. We have selected 'Minerals' for this demonstration.

The lower drop-down menu lists different minerals in alphabetical order. We're going to look at quartz. Once the specimen has been selected, a series of buttons and a description of the mineral appear below the two drop-down menus, as shown here for quartz. Several views and, in most cases, a video clip of a rotating image, are available for each specimen. Finally, a 'Mineral properties' page is given for each mineral.

For this demonstration, we'll look at the 'Crystal cluster' view. Each view has a short description, which appears below the menus. The main window shows the full specimen view, when initially selected from the menu. At the centre of the field of view, at any magnification, is a small cross or cross-hairs.

The coordinates of this cross are constantly displayed below the viewing window, as x- and y-coordinates. The sample can be moved to a specific location by typing its x- and y-coordinates into the empty boxes, and clicking the 'Go' button. This useful feature allows locations of particular features to be communicated between different users.

The image can be manipulated either by zooming in or out or by panning around the specimen, at different magnifications. As the main image is zoomed or panned, the inset image in the bottom right-hand corner shows its location as a red rectangle. The dimensions of the field of view displayed are given in millimetres, below the inset image. These will change as you zoom in and out.

The image can be moved either by clicking and dragging the image itself or by clicking and dragging the red rectangle in the inset image. The image magnification can be varied by zooming in and out of the field of view. This is done with a simple zoom slider control, which magnifies the area around the cross-hairs.

The slider dot can be dragged or, alternatively, you can click to the right or left of the zoom dot to zoom in and out of the specimen. If you wish to zoom into another area, simply drag the image, so that the area is located on the cross-hairs, then zoom in. The five millimetre scale bar at the bottom left-hand corner of the viewing window shows millimetre increments. Its size adjusts as you zoom in and out.

We recommend that you try out all these controls to familiarise yourself with them before you start any activities. Below the viewing window, on the left-hand side, are two tick boxes. When the 'Labels' box is selected, labels are superimposed on the specimen, identifying particular features. These labels are shown only at the lowest magnification.

If the 'Labels' box is clicked when at a higher magnification, the image reverts to the lowest magnification and the labels are shown. When the 'Measure' box is selected, you can click on the image and drag out a line in any direction, allowing direct measurement of features anywhere on a specimen. To get rid of the measurement, deselect the 'Measure' box.

When a 'Video of rotating specimen' button is selected, a video clip window replaces the zooming and panning window. The button at the bottom left starts and pauses the video clip. Finally, when the 'Mineral properties' button is selected, a range of key data for that mineral are displayed.

In addition to the minerals, the Digital Kit also contains rocks and fossils. These can be viewed in the same way as the minerals. In the fossils part of the kit, different views of the same specimen are indicated by A, B and C, and so on, after the name. Some fossils in the kit are replicas and are shown in black and white in order to distinguish them from real specimens, which are shown in colour. Replicas are also indicated by an R after the name.

Now that you know what the Digital Kit can do, I would suggest that you explore some of the different specimens, to familiarise yourself with the system and its functionality. This will help when you have to use it to work through any activities that make use of it.

End transcript: Video 1 Introduction to the Digital Geology Kit.

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Video 1 Introduction to the Digital Geology Kit.

Interactive feature not available in single page view (see it in standard view).

Question 1

Select the specimen 'Variety amethyst' from the 'Quartz' list of minerals in the Digital Geology Kit. How long is the amethyst crystal on the far left? Measure it using the graticule.

Answer

It is about 16 mm. Note that there are large divisions on the graticule every 10 mm.

Question 2

Now go to 'Red crystals in gneiss' in the 'Garnet' list. Go to coordinates X = 1860, Y = 930. (Note that, hereafter, the X and Y labels will be omitted on all coordinates, e.g. this point would be '(1860, 930)'.) Is any red garnet visible at the point denoted by the cross hairs?

Answer

No, garnet is not visible at this point; only a white mineral is visible at the stated coordinates.