Perhaps this is a crystal which is cut differently than the HF ones?
For example, the 32.768kHz watch crystals.

On Wed, Sep 16, 2009 at 9:27 PM, John Coppens <john@jcoppens.com> wrote:
> On Wed, 16 Sep 2009 18:45:43 +0100
> Peter Restall <pete@restall.net> wrote:
>
>> I was playing about with some low frequency crystal filters at the
>> weekend (60KHz - it's the ongoing epic that is my MSF receiver :) and I
>> was just wondering if anybody out there has any good sources of
>> information that they can point me to - specifically LF crystal filters
>> and their nuances. =A0There's tons of info on the 'net about MHZ region
>> stuff, including Wes Hayward's articles - all very useful if I was
>> building a higher frequency filter.
>
> I have never heard about 60 kHz crystal filter. I'm quite sure those are
> "mechanical filters", but not piezoelectric.
>
> If I'm not mistaken they have mechanically resonant cavities, and
> electromagnetic 'launchers', quite low-impedance.
>
> Normal crystal have way too high Q to make a practical filter at that
> frequency (say Q of 40000, would give a filter of only 1.5 Hz!)
>
> John
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