Pressed meerschaum was very prevalent in the first half of the 20th century. It was called chip meerschaum, and they were carved as well turned. It was generally not intended to deceive, it was usually advertised as exactly what it was and marketed as lower cost alternative to the pricier block meerschaum.
The tongue test will only work a clean chamber. If there is any cake or combustion residue don't count on it working. Weight is subjective, yes on average pressed meer pipes are heavier than block pipes. But unless you've handled a fair number of old meers your basically just guessing. Old chip meers can be deceptively light.
It is true that chip meer does not color or colors very poorly. But the one thing I have noticed with pressed vs block is the way they cut with tools. Having replaced tenons in chip meer pipes I noticed that it has very coarse sandy feeling when you run a tap into it or scrape it with a blade as apposed to block which has very uniform soft powdery feeling. Chip meer also has a different sound and feel when you tap on it with something hard.
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