What's the difference between "kind" and "type"?
For example:
This is some type of mushroom.
This is some kind of mushroom.
There are different types of books.
There are different kinds of books.
I think that they are all valid sentences, but somehow I have the impression that a type is a bigger group than a kind.
Is this correct?
In short, type is used to differentiate one group from the rest and kind is used to link an individual to a group. They are sometimes interchangeable, but not always.
Type refers to clearly distinguishing and essential characteristics or traits shared by members of a group. Its root meaning is "impression."
O+ is the most common blood type in the United States of America.
To mankind in general Macbeth and Lady Macbeth stand out as the supreme type of all that a host and hostess should not be — Max Beerbohm.
Kind, on the other hand, usually refers to a group trait that is shared innately by the members (see "mankind" above). Its root meaning is "race" or "offspring."
The true test of civilization is, not the census, nor the size of the cities, nor the crops, but the kind of man that the country turns out — Ralph Waldo Emerson.
The rule which forbids ending a sentence with a preposition is the kind of nonsense up with which I will not put" — misattributed to Winston Churchill.
Interchangeable use:
She's not that kind/type of person. She is not nasty. She's very nice.
See examples below:
She's not my type. (=I'm attracted to a different kind of girl)
She's not your kind. (=She's a fundamentally different sort of person)
See link1 and link2.
I'm afraid it's rather nebulous and very context dependent. Both can be very general or very specific depending on what you're talking about. For this kind (or type) of general purpose use you can regard them as equivalent.